Browsing by Person "Zebitz, Claus P. W."

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Characterization of mechanisms of resistance to common insecticides in noctuid pest species and resistance risk assessment for the new lepidopteran specific compound flubendiamide
(2009) Konanz, Stefanie; Zebitz, Claus P. W.
Noctuid species, such as the beet armyworm Spodoptera exigua, the cotton bollworm Helicoverpa armigera and the tobacco budworm Heliothis virescens, are well-known pests in many agricultural cropping systems worldwide. The extensive and widespread use of insecticides against these species has led to the development of resistance against almost all commercially used compounds. The focus of this thesis was on the novel lepidopteran specific compound flubendiamde, to get a detailed overview about the efficacy using different kinds of bioassays for a resistance risk assessment. On the other hand, the underlying possible resistance mechanisms of a S. exigua strain from southern Spain was investigated on the toxicological, biochemical, pharmacokinetic and molecular level. The basic of all further experiments was two bioassay techniques, a leaf-disc spray application and an artificial diet bioassay, on 2nd instar larvae. Flubendiamide and 11 competitors with different mode of actions were tested on three susceptible laboratory strains (HELI-AR, HELI-VI, SPOD-EX S) and one field strain from Spain (SPOD-EX E-98). The aim was to get baseline susceptibilities of the three noctuid species and additionally the resistance profile of strain SPOD-EX E-98 against the different insecticides. The results of the two bioassay techniques were comparable with each other, emamectin shown the highest efficacy followed by low EC50-values for flubendiamide, deltamethrin and indoxacarb. The robust artificial diet bioassay was used for a worldwide resistance monitoring for flubendiamide, and resulting in a mean efficacy of 93% in 18 test populations. An interesting cross-resistance pattern against insecticides with different mode of actions demonstrated the S. exigua strain SPOD-EX E-98, and can be called as ?multi-resistant?. High resistance to three classes of insecticides, pyrethroids, benzoylphenyl ureas and carbamates/organophosphates, was detected in this strain, also moderate resistance levels to endosulfan and indoxacarb. The in vivo application study with the synergist PBO (monooxygenase inhibitor) has shown an additionally participation of this enzyme system towards the deltamethrin resistance in this strain. Additionally, PBO and two esterase inhibitors had no effect to the resistance level of triflumuron (benzoylphenyl urea) and so target-site resistance is likely in this case. Using molecular biological methods, a point mutation (kdr) in the voltage-gated sodium channel of the resistant strain SPOD-EX E-98 was detected, this channel is the target of the pyrethroids. This target-site resistance is particularly responsible for the extremely high resistance factor (~900) of the pyrethroid deltamethrin detected in the bioassays. In order to investigate the pharmacokinetic profiles of deltamethrin, triflumuron and flubendiamide in S. exigua larvae radiolabelled compounds were used. No differences in penetration or excretion of the compounds were observed between the two strains. This suggests that physiological changes have not influence as a possible mechanism of deltamethrin and triflumuron resistance. Four biochemical markers, carboxylesterases (CEs), cytochrome P450-dependent monooxygenases (monooxygenases), glutathione S-transferases (GSTs) and acetylcholinesterases (AChEs), were investigated in both S. exigua strains. These enzyme systems are known to be linked with metabolic detoxification/resistance to diverse insecticides. With the exception of GST, in the multi-resistant SPOD-EX E-98 strain was found significantly higher enzyme activities to the other three marker enzymes. The higher CE activity in the multi-resistant strain SPOD-EX E-98 was further investigated, using an nPAGE to obtaining the iso-enzyme banding patterns of both strains. In comparison, the strain SPOD-EX E-98 exhibited an additional thick band and it was not possible to inhibiting this band in vitro through the esterase inhibitor DEF. It is possible that this result is involved in resistance, but only further investigations could be clarify the exact role of the additional band in this resistant strain. The AChE of both S. exigua strains was used for in vitro inhibition studies. The resistant strain SPOD-EX E-98 was insensitive against several organophosphates and carbamates compared with strain SPOD-EX S. Only one exception was detected, the AChE of the resistant strain was more sensible to carbofuran than the enzyme from strain SPOD-EX S. This phenomenon of ?negative cross-insensitivity? is generally correlated with an altered substrate binding site of the AChE. Further investigations of kinetic parameters exhibited a higher turnover of the substrate in strain SPOD-EX E-98. The bioassays confirmed these results and so the resistance mechanism of the two chemical classes is an altered AChE in the resistant strain.
Effect of mulch application in combination with NPK fertilizer in cowpea (Vigna unguiculata (L.) Walp.; Leg.) on two key pests, M. vitrata F. (Lepidoptera: Pyralidae) and M. sjostedti Trybom (Thysanoptera: Thripidae), and their respective parasitoids
(1999) Zenz, Nikolaus; Zebitz, Claus P. W.
African farmers use mulch to preserve soils from physical and nutritional degradation. No clear evidence exists whether mulch may also be used successfully to control pests. This study aimed to assess the effect of mulch in combination with NPK fertilizer on two key pests of cowpea (Vigna unguiculata (L.) Walp.; Leguminosae), the legume pod borer Maruca vitrata F. (Lepidoptera: Pyralidae) and the flower thrips Megalurothrips sjostedti Trybom (Thysanoptera: Thripidae), inclusive of their parasitoids. Trials were carried out in three regions of Benin, West Africa, from 1995 to 1997. This study focused on plant physiology, soil properties, climate as well as habitat structure, all of which were assumed to have a strong influence on pest abundance. Data on plant development represented by number of nodes, flowers, and pods were collected periodically. Flowers were sampled in parallel to monitor the abundance of both pests. Eggs and living larvae of M. vitrata and larvae of M. sjostedti were collected periodically and reared for studies on parasitism. Mortalities due to three braconid parasitoids were assessed belonging to the order of hymenoptera, Dolichogenidea sp., Phanerotoma leucobasis Kriechbaumer, and Braunsia kriegeri Enderlein, which represented the dominant species on larvae of M. vitrata. Ceranisus menes Walker (Hymenoptera: Eulophidae) was the only parasitoid found on M. sjostedti. Pods were harvested and assessed for damage of M. vitrata. Pod number, weight per pod, relative pod and grain damage were investigated and estimates were made of the yield losses. Yield of cowpea was measured and related to preceding pest abundance. Pods were counted, weighed, and husked, and grains were weighed. Flowers were collected from potential wild host species of both pests in the vicinity of cowpea fields. Insect counts from flowers in the adjacent cowpea fields served as comparison.
Freisetzung von Neonicotinoiden aus der Saatgutbeizung in Guttation von Kulturpflanzen und deren Auswirkungen auf Honigbienen Apis mellifera L. (Hymenoptera: Apidae)
(2015) Reetz, Jana E.; Zebitz, Claus P. W.
Seed coating with the systemic neonicotinoids clothianidin, imidacloprid, and thiamethoxam was considered environmental justifiable and no side effects on non-target organisms such as honey bees were considered during the registration process as seed coatings. In 2008, sowings with neonicotinoid-coated corn has caused severe damages on honey bee colonies in the upper Rhine Valley, Germany. As a consequence, the seed coating with neonicotinoids in maize and wheat was suspended in Germany in May 2008; since May 2013 there is a temporary ban of the three neonicotinoids by the EU Regulation No. 485/2013. The release of systemic active substances (a.s.) in guttation of seed-coated plants, e.g. winter oilseed rape (WOR, Brassica napus L.), represents a possible contamination source for non-target organisms and could actively be used as a water source by honey bees (Apis mellifera L.). The occurrence of guttation was examined and sampled under field conditions in maize, xtriticale and WOR. The residual analysis of guttation from seed-coated WOR revealed the release of residues up to 130 µg a.s. L-1 in autumn (Reetz et al. 2015). However, even the highest residues in WOR guttation are considerably lower than those in guttation of maize (up to 8,000 µg a.s. L-1) or xtriticale (up to 1,300 µg a.s. L-1; Reetz et al. 2011). In spring, the released residues in WOR guttation are lower than in early autumn (~30 µg a.s. L-1) and continue to decline steadily until flowering. Considerable high amounts of residues have been released by maize (spring crop) over a long period of the crop cycle. Laboratory investigations (according to OECD-Guideline 213) showed that feeding of isolated honey bees with a sugar/guttation-solution from seed-coated WOR leads to a mortality less than 20 % (Wallner et al. 2012), but this way of exposure is not similar to the situation of water foraging honey bees. Observations of water foraging honey bees in the field are nearly impossible. Therefore, honey-sac content of foragers returning to the hive were analysed for residues (Reetz and Wallner 2014). These experiments showed that on the one side the weight of honey sacs is lower during autumn at the same time when high residues in guttation of seed-coated WOR occur than in summer, and on the other side, that the intake of water is increased by the factor of 25 compared to the amount of nectar, which seems to be associated with the absence of nectar sources during autumn (Reetz et al. 2012). There seems to be no exclusive season- or daytime-depending water collecting activity in honey bee colonies in temperate zones. Therefore, the collection of guttation from seed-coated plants by foraging honey bees is likely. However, during summer and the periods of high nectar flows honey bees might gather rather runny nectar as a replacement for water than WOR guttation. Honey bees gathering on WOR guttation were just occasionally observed in a small-patterned landscape, but more frequently in the field site with intensive agriculture and a reduced variety of alternative water sources. HPLC-MS-analysis of honey sacs (n= 204) reveal that residues of thiamethoxam are detectable in 19 % (n= 38) of the honey-sac contents with a range of 0.3 to 0.95 µg a.s. per litre (LOQ= 0.3 µg a.s. L-1; Reetz et al. 2015 accepted). In 12 % (n= 24) of the samples, thiamethoxam could be detected in concentrations below LOQ. Clothianidin and its metabolite TZMU were measured in one sample each (0.5 %) at concentrations below LOQ (clothianidin) and LOD (TZMU), respectively. Based on these experiments, it has been proven that honey bees use guttation of seed-coated WOR as water source in absence of alternative nearby water sources. Thus, during a short period of about a few weeks in autumn, when the highest residues are released in WOR guttation, there might theoretically be a risk for single honey bees. Guttation of xtriticale and WOR is just temporary present in the field, whereas guttation of maize is present in the leaf sheaths during the day due to the funnel function of the maize leaves. Additionally to theses facts, there is a low water demand in honey bee colonies during autumn in contrast to the occurrence of maize guttation, which occurs at the same time when honey bee colonies raise and have an increasing demand of water. The current evaluation of short-term effects of chronic exposure to sublethal concentrations of neonicotinoids in pollen on honey bees at colony level is based on the application of higher concentrations (2 ppb clothianidin; Sandrock et al. 2014) than detected in the honey-sac contents of the water foraging honey bees in this experiment (< 1 µg a.s. L-1; < 1 ppb). Based on these threshold values for side effects by chronic feeding of neonicotinoids, the concentrations of residues measured in the honey sacs of water foraging honey bees seem to have still less potential for side effects on single honey bees or on colony level.
Functional larval-parasitoid biodiversity in apple orchards as benchmark for management intensity and potential instrument for ecological amelioration of Iranian apple production
(2019) Lashkari-Bod, Abdullah; Zebitz, Claus P. W.
Although a consensus through the concept of sustainable agricultural production and its indicators to assess its functionality varies, it is expected to be long-term and reliable. The sustainability would change temporarily and spatially. It is influenced by political, social and economical is-sues, which reveals its interdisciplinary essence in concert with farming strategies and practices to produce human food. The management of plant protection is capable to impose unsustainability into farming system. The frequency and intensity of unsustainable practices would result into devastating effects on diversity and abundance of beneficial arthropods. The communities of natural enemy may promote sustainable management, but the anthropogenic interventions such as broad-spectrum pesticide applications would distort the essence of self-monitoring of natural invertebrates as regulators. The conventional agricultural management makes the habitats to be simplified through food webs and ecological complexities, which lead to species loss (extinction or emigration) and consequently to species interactions (connectance). The ecologically based management such as integrated pest management (IPM) would focus to maintain species and increase diversity in natural communities, which contributes to sustainable approach as alternative versus conventional agriculture. The negative effects of chemical pesticides would dramatically decline the ecosystem process and affect the energy flow among different trophic levels, which is manifested as functional rates in local or regional scale of ecosystem. The human-manipulated areas create negative consequences on the ecosystem functionality through vanishing the key natural resources (i.e. shelter, food provision, and alternative host prey), which affect maintaining natural enemy communities. The complementarity effects of antagonist communities can lead a synergetic impact on pest control, when biodiversity is conserved through vegetation, rational bio-pesticide application, and ecological infrastructure, the functional traits (richness and evenness) among interacting species will be improved. Furthermore, the intensified agriculture would arise pest outbreaks or convert a secondary and unimportant pest into a serious one. The antagonistic communities may represent as bio-indicators. The presence or absence of higher trophic levels and their complexes would reflect biotic or abiotic changes in the environment, which would eventually be expressed as parasitism or consumption rate. The scope of current research is limited to indicators of sustainability through pest management and does not comply a holistic approach on ecological, political, social, and economical managements. The preliminary results focus on the status quo of plant protection in Iran and biodiversity indices in Germany used to compare the different farm systems to show how the management can affect the community components and their interactions. The environmental and anthropogenic impacts on biodiversity of beneficial arthropods in different orchard management conducted in Germany, where the accessibility of abandoned apple orchards is more prevalent than Iran. To evaluate the impact of conventional intensive management vs. ecologically based sustainable practices on invertebrate beneficial community, a comparative study was conducted to assess food web pattern of larval-parasitoid communities, biodiversity indices, and parasitism rate in response to apple orchard by four different managements. Field samplings were occurred during 2011-2015 in Baden-Württemberg, Germany. The orchard managements were distinguished based on the frequency and intensity of pesticide applications into the farming system. The categories of orchard management were managed (organic and integrated), and Streuobst (semi-abandoned orchard), which were situated in Denzlingen, Emmendingen, Goldener Grund, Hohenheim research center, Ilsfeld, Lake Constance, Neuhausen, Plieningen, Rommelshausen, and Scharnhausen. The sampling was conducted by installation of corrugated cardboard and random observation to collect larval caterpillars (Tortricidae and Gelechiidae). The collected samples were transferred to lab to rear adult parasitoids and further studies on taxonomic affiliation. Out of 7,923 healthy host larvae collected, totally 324 parasitoid individuals from three sub-families of Braconidae, Ichneumonidae, and Perilampidae were found. Four parasitoid species were found positive host-density dependent, the rest of the parasitoid species showed no densi-ty-dependency or were found in too small numbers. The highest richness, abundance, and evenness of larval-parasitoids were found in Streuobst orchards (i.g. Plieningen), which received no to minimal pesticide inputs. The interaction diversity of food webs (connectance) in Streuobst showed the highest number of trophic links in response to other orchard managements where the commercial (conventional) orchards harbor no to the least biodiversity indices of beneficial arthropods. Percentage similarity also assessed to depict the similarity of larval-parasitoid community structures in different managements. It was revealed the orchards with the same management contain similar parasitoid compositions. To describe and analyze the information on apple growing management, circumstances of plant protection, pest status, and major obstacles to initialize sustainable production in Iran, a questionnaire was designed to survey 39 apple growers from East-Azerbaijan, Fars, Isfahan, Tehran, and W. Azerbaijan in July 2014. It was found that management of the orchards mostly is under the supervision of the apple growers. Farmers in Isfahan suffer a road infrastructure to have an access to the nearest market to sell their product indicating an economic monopoly. The distance to experts affects the intensity of pesticide application by farmers. The conventional agriculture is prevailing in all provinces and access to bio-pesticides highly limited to Tehran. Totally 29 pesticides were used against different fruit pests in Iran. The most damage intensities occurred by pests in province scale and weeds in regional scale. The outbreak of secondary pest Tetranychus urticae as key one indicates human perturbations in Iran’s farming system. Tehran province enjoyed diverse apple cultivars contrary to other provinces, which are poor in diversification. The predominant outlook to choose a cultivar among apple growers was marketing.
Inter- and intraspecific variation of nutritional and environmental adaptation of egg-parasitoids of the genus Trichogramma (Hymenoptera, Trichogrammatidae)
(2013) Alkarrat, Hamdow; Zebitz, Claus P. W.
The biology and the use of egg parasitoids of the genus Trichogramma (Hymenoptera: Trichogrammatidae) as a biological control agent has been studied since 1904 and more than one thou-sand scientific papers on Trichogramma have been published. However, there are still open questions about the impact of biotic and abiotic environmental factors on the biology of these beneficials, such as nutritional ecology, diapause, cold storage, plant-pest-Trichogramma-interactions, and, particularly, the intraspecific variation of environmental adaptations. These parameters can seriously affect the effectiveness and the practical application of these parasitoids in many crop production systems. In this study, we have investigated the effect of: (i) different of diets, (ii) properties of pest?s host-plant surfaces and (iii) overwintering and cold storage on the performance of different species and strains of Trichogramma to select the best candidate for biocontrol of the Codling moth, taken here as a model target. Experiments with different diets (honey, pollen and honey with pollen) were carried out and their effects on life-table parameters of four strains of Trichogramma cacoeciae Marchal (HOH 1, HOH 2, KIO 2 TN and SY 98 01), and one strain of T. evanescens Westwood (195 DE 06) and T. oleae Voegelé (See 2) was evaluated under laboratory conditions. Honey diet im-proved significantly adult mean longevity, mean fecundity, mean fertility, and net reproduction rate (R0). Significant intraspecific variability was shown only in mean fecundity and mean fertil-ity, but not in longevity. The best performing strain of T. cacoeciae (HOH 1) in these experi-ments has been taken to assess the nutritional value of pollen collected from birch, maize and sunflower. Pollen as honey additive had a significant positive effect on female longevity as com-pared to honey alone, but longevity did not differ significantly between the honey-pollen diets. Pollen added to water had no ameliorative effect on longevity except sunflower pollen, which had a significant detrimental effect. Mean total fecundity and fertility of females was not im-proved when fed honey and birch or maize pollen. Sunflower pollen added to honey, however, had a pronounced detrimental effect on these parameters. When these three pollens were offered with water, all parameters were not or negatively affected, revealing sunflower pollen having the worst nutritional value. Tests on the suitability of bee-pollen to ameliorate Trichogramma mass-rearing were done with T. cacoeciae, T. evanescens and T. oleae. Except fertility, longevity and fecundity differed significantly between the species. Basic diet (water or honey) and pollen added showed interactive effects on the performance of Trichogramma species. Interactions between species and added pollen only revealed significant differences in fecundity and fertility, whereas longevity was only slightly affected. Species - basic diet - pollen interactions could only be shown for fertility. Trichogramma oleae had a shorter adult lifespan and the lowest number of parasitized eggs compared with the other two species, but it had the highest rate of emergence when fed on honey mixed with bee pollen. The results indicate that (i) Trichogramma adults are feeding upon pollen, and (ii) nutritional quality of pollen differs significantly between plant spe-cies, and (iii) honeybee-pollen may be used to improve mass-rearing of Trichogramma species. Properties of the pest?s host-plant surfaces (apple, cv. ?Golden Delicious?, ?Boskoop? and ?Topaz?) were evaluated in their effect upon searching behaviour and foraging success of three strains of T. cacoeciae (HOH 1, KIO 2 TN and SY 98 01) when eggs of the Codling moth, Cydia pomonella (Lepidoptera: Tortricidae) were offered as hosts. Foraging time differed significantly between the strains tested, showing strain HOH 1 performing best. Host handling time and time spent post-parasitization did not differ between the strains. The apple cultivar did not affect any of these parameters. Leaving time was significantly affected by chemical cues comprising lepidopteran egg and scale volatiles or contact chemicals, host pheromones, host frass or female moth accessory gland secretions abundant on the leaves, where giving up time was shortest on blank leaves and, compared to blank leaves, significantly longer on leaves with adult stimuli only but no host eggs. Leaving time was further affected by apple cultivar and T. cacoeciae strain tested. Compared with the other cv. tested, time spent on leaves of cv. ?Golden Delicious? was longest for any treatment. Trichogramma cacoeciae strain HOH 1 always spent the shortest on any cultivar and treatment. In another experiment, parasitization of eggs on apples placed at different heights (0, 25, and 50 cm above cage ground) was assessed. The parasitization rate of Cydia eggs was slightly affected by apple varieties; however the differences were not consistent. Parasitization rates decreased with height of apples above ground, with the highest rate on apples placed on ground, near the releasing point of Trichogramma females. Significant differences in parasitization rates between strains could be detected, but they were not consistent also. One German and one Tunisian strain of Trichogramma oleae and two German, one Tuni-sian, and one Syrian strain of T. cacoeciae were hibernated from October 10th 2007, up to parasi-toid emergence in 2008 under field conditions in Stuttgart-Hohenheim, Germany. 60 days after exposure to outdoor conditions and after complete hibernation life table parameters of survivors was assessed. Our results demonstrate that all strains studied were able to overwinter successful-ly on eggs of the factitious host Sitotroga cerealella Olivier (Lep.: Gelechiidae). Mean develop-ment time of trichogrammatids until adult emergence after full hibernation ranged between 183 and 189 days. Emergence rate ranged between 53.59 and 60.98 %. Net reproduction rate (R0) of T. oleae strains decreased with duration of field exposure, whereas in T. cacoeciae strains R0 was lowest after 60 days field exposure. Longevity of all adults emerged from parasitized eggs was affected by field exposure compared to the control. Total fecundity, total fertility and percent fertility after 60 days and/or after hibernation showed neither significant difference between strains nor within the strains studied. Total fertility of T. cacoeciae strains decreased significantly after midterm and/or after full hibernation compared with the control, while no significant differences were detected within T. oleae strains. Time until adult emergence, mortality, and percentage of deformed adults increased with storage duration at 4 °C. Trichogramma oleae (German strain) showed best adaptation to cold storage for 50 days. Finally and based on this study, our data suggest that the diets of honeybee-pollen could be used as food to improve Trichogramma mass-rearing, and also the German candidate T. cacoeciae HOH 1 could be a potential candidate for future mass rearing and field release programs for biocontrol of different lepidopteran pests in orchards. Furthermore, it could be proved that even allochthonous Trichogramma species / strains originated from countries with a higher annual average temperature (Syria and Tunisia) are theoretically able to establish and survive winter conditions in southwestern Germany. At least this possibility requires an environmental risk-analysis for these species/strains or any potential other Trichogramma species intended to be used as biocontrol agent in Germany.
Laufkäfer(Col., Carabidae) in Feldhecken Südwestdeutschlands : Vergesellschaftung und Biodiversität in Abhängigkeit von der Habitatqualität
(2013) Theves, Florian; Zebitz, Claus P. W.
The drastic decline of species caused by intensification of farming in the long run reduces the flexibility and productivity of our agroecosystems. One possibility to counter this negative development is the preservation of typical local species compositions in anthropogenic cultivated ecosystems. The conservation of valuable, or the creation of new habitat patches is a way to maintain these requirements. So far, there is too little knowledge yet, which habitat traits are most important for a given group of organisms. As the habitat requirements of many species vary on a regional level, it is necessary to categorize biotopes into types as a precondition for the application of those types on a broader scale. In this study, the zoo-ecological value of hedgerows is categorized by using ground beetles (Carabidae). Using the ?Filderebene? south of Stuttgart as an example, multivariate methods were used to distinguish general types of hedgerows to which regional bioindicators are assigned. Furthermore, the components of ground beetle diversity in hedges are investigated on different spatial scales and a method to estimate functional diversity is tested. It has been demonstrated that hedgerow types can be distinguished by a gradient of ground area size and age. Each of these types contain specific species, suitable for differentiation, established by calculation of species-associatons and indicator-analyses. While richness in species and individuals alone shows no clear dependency, especially forest carabids were positively correlated with hedgerow size. Besides, species-accumulation-curves show that few large hedges contain more species than small ones. Furthermore, it could be proven, that the carabid beetle associations are not only affected by the factors size and age, but also by the coverage of herbaceous vegetation and zonation of the hedgerows. The biodiversity components show a dependency on hedgerow size, too. While alpha-diversity per hedge increases significantly with decreasing area, beta-diversity decreases simultaneously. This relationship can be explained by the immigration of field species into the small hedges, whereas large and old hedges have a greater variety in structure, which results in a large number of microhabitats occupied by carabids. On site-level, the large hedges showed a higher alpha- and gamma-diversity than small hedges, which can be attributed to a higher general species richness of sites with extended hedgerows. In small hedges, biodiversity depends on the surrounding crops, whereas carabid beetle associations of large hedges are less affected by bordering habitats. This was evident, because homogenization of the surrounding crops caused a decline of alpha-diversity and an increase of beta-diversity in the hedges. A comparison between beta-diversities at site- vs. hedgerow-level shows higher heterogeneities inside than between hedges. In order to consider the functional component of biodiversity as well, the carabids of the hedgerows were partitioned into functional groups (guilds) by means of cluster-analysis based on their morphological and ecological traits. The number of guilds in a hedgerow can be used as an estimate for its functional diversity and efficacy of resource use. The average number of three guilds per hedge varies with hedgerow size and age. This results in a shift of species composition of carabid guilds based on hedgerow type and the continuity, of the functional groups occurence during the investigation period. In smaller hedges, the guild of ?forest species? is substituted by less specialized field species and the number of different significant guilds is less stable than in larger hedges.
Leg attachment and egg adhesion of the codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) to different surfaces.
(2014) Al Bitar, Loris; Zebitz, Claus P. W.
Adults of Cydia pomonella live on host plant surfaces, differing considerably in their structural, chemical, and physicochemical characteristics according to host plant species, cultivar, plant organ, phenological stage, environmental conditions, and orchard management practices. This variable world provided by plant surfaces can profoundly affect many aspects of insect–plant interactions, such as attachment, locomotion, oviposition site selection, egg adhesion, and also survival of adults and their offsprings. Despite their importance, little attention has been given to the structural and wetting properties of the codling moth’s host plant surface and their effect on insect–plant interactions of this important pest. Therefore, studies in this thesis were undertaken to investigate the effect of structural and physicochemical characteristics of the substrate on two main codling moth-plant interactions: (1) the attachment ability of adults, and (2) the adhesion of their eggs. The first part of this thesis was performed to (1) analyze tarsal morphology of male and female C. pomonella to know more about their pretarsal attachment devices, and (2) to investigate their attachment ability on a variety of smooth and rough substrates, using a centrifugal force device. On all smooth artificial substrates tested, both sexes of C. pomonella adults achieved excellent attachment ability, by means of their smooth, flexible and well developed arolia. Hydrophobicity of the substrate had no considerable effect on friction forces. Cydia pomonella females showed a very good attachment ability to the smooth Plexiglas substrate in both horizontal and vertical positions. Thus, it can be concluded that the attachment system of C. pomonella is rather robust against physicochemical properties of the substrate and is able to achieve a very good attachment on vertical and horizontal plant surfaces. Results on the epoxy resin substrates, differing only in surface asperity size ranging from 0-12 µm revealed that the attachment ability of both sexes was significantly affected by surface roughness. Maximal friction force was measured on the smooth substrate whereas minimal friction force was assessed on microrough substrates with 0.3 µm and 1.0 µm size of asperities. On the remaining rough substrates, friction forces were significantly higher but still lower than on the smooth substrate. Both sexes generated similar friction forces on the same substrate, in spite of the considerable difference in their body mass, suggesting that both sexes attach effectively to variable rough plant surfaces in their habitat. However, since smooth surfaces have been reported previously to be the most favorable substrates for ovipositing females of C. pomonella, it is possible that they use their attachment system to sense the substrate texture and prefer those substrates to which their arolia attach the best. A better survival of the codling moth offspring is assumed to be ensured by the selection of suitable oviposition sites by females, as well as by a proper adhesion of deposited eggs to these sites. In apple orchards, eggs of the first generation of the codling moth are laid on leaf surfaces in the vicinity to small fruits, later in the growing season, most eggs are deposited directly on fruits. In the second part of this thesis, egg adhesion of the codling moth to different leaf and fruit surfaces of the domestic apple was investigated by measuring the pull-off force required to detach the eggs from the plant surface. Morphology, wettability, and free surface energy of the tested plant surfaces were analyzed to evaluate their role in egg adhesion. Furthermore, eggs and their adhesives covering leaf or fruit surfaces were visualized. Eggs on the smooth upper leaf sides of the tested cultivars were easily detached, requiring similar pull-off forces (total average of 6.0 mN). Up to 2-3 times stronger pull-off forces had to be applied to detach eggs from the trichome-covered lower leaf side, and these forces differed significantly between cultivars, owing mainly to different trichome covered areas. Whereas on the waxy fruit surface of all apple cultivars tested, eggs were very tightly adhered, and required 4-10 fold stronger pull-off forces than those previously measured on upper and lower leaf surfaces of the identical apple cultivars. Cydia pomonella eggs adhered stronger on the upper and middle fruit sections of all cultivars tested, than on the lower section. The influence of plant surface properties on egg adhesion, as well as the mechanisms used by the moth to overcome the presumable anti-adhesive properties of apple fruit surfaces, were discussed. Additionally, the results were debated in the context of the oviposition site selection, female attachment, as well as offspring survival of the codling moth.
Modeling population dynamics and dispersion of Codling moth Cydia pomonella L. (Lepidoptera, Tortricidae)
(2009) Gharehkhani, Gholamhossein; Zebitz, Claus P. W.
The study of insect dispersal plays an essential role in estimating the spread of damage caused by a newly invaded pest or the spatial distribution of an insect during the active period in growing season. Moreover concerning dispersal, quantitative information performs a crucial role in the evaluation and implementation of pest control. Since rearing clean and healthy insects in sufficient numbers is the most important prerequisite for many basic research programs and for developing pest control strategies, mass rearing of the Codling moth on the artificial diet carried out as the first step at optimum conditions. With regard to the fundamental function of feeding and pre-releasing handling on insect biological attributes, we intended to evaluate the individual marking influence on longevity of Codling moths in the next step. For this purpose, one day old adult male and female moths were kept three and five minutes at -20°C to make them motionless, then immediately marked individually with felt tip pens and coded by the different colors, maintained under optimum condition and checked daily for 13 days. The proposed linear model accounted for 89 % of the variations. Numbing and marking process influenced of the moths longevity regardless of their sex while the duration of the anesthetize does not affect the survival of moths meaningfully. Regarding the obstacles associated with egg and pupa storage of Codling moth, we examined the possibility of adult moth?s storage in low temperature in order to evaluate its eﬀect on longevity of moths. Adult 12-24 h old male and female moths were treated separately and maintained in 4 ◦C and (0:24 h, L:D) photoperiod during the entire adult life. The survival rate evaluated with two days interval throughout 27 days. The effects of day and treatment were significant. It seems that the female moths tolerate the cold condition better and further than the male moths and live longer. Additionally the proposed models accounted for 71 % and 57 % of the variations for male and females respectively as verified more affection and debility of the males by the storage condition. Disadvantages of individual marking led us to test the mass marking and it?s influence on the survival of the moths. One-day-old moths were marked with fluorescent powder. Mortality of the males and females recorded daily for a 20 days period. Results indicated that the effects of the sex, the replications and interaction of them were significant as well as the effect of the day. The model accounted for 96 % of the variations. This study indicated that male and female moths were inﬂuenced by the ﬂuorescent powder. Findings of this study may facilitate the improvement of mark-release experiment results and interpretation more precisely in particular for dispersal studies. In the field experiments, firstly trade off trap structure in assessing the horizontal and vertical distribution of Codling moth carried out as well as outward and inward dispersal. Three different types of the traps including Delta pheromone traps, Delta Pear ester trap and Cylinder shape Pear ester traps were used in the research station of the Hohenheim University. Ninety six traps were suspended in eight compass directions in order of four traps per direction, at three heights in random arrangement in outward dispersal. In inward dispersal study the traps arrangement and number was the same but dissimilarly the releasing site was from borders of directions SW, NW, W, E, and SE. The traps were checked daily and followed nine days after release. Results demonstrated no significant differences between three types of traps in attracting the marked and feral females ?Fn?. Meanwhile significant dissimilarity in marked and feral male ?Mn? catches were traced. Reaction of the moths to the traps elevation was not similar in the vertical distribution study. whereas marked female moths exhibited significant differences to different heights, marked and feral male and ?Fn? moths revealed no difference reaction to traps in different heights.In horizontal distribution study marked female moths ?Fr? exhibited significant differences. It is revealed that dominant directions for marked and feral moths were different. Concerning inward distribution, both marked male ?Mr? and female demonstrated significant differences in their direction and distances. In regard to this findings and priceless and effortless manufacturing of the Cylinder traps, utilization of this trap in mark-release-recapture studies of female and male Codling moths is recommended. Effect of apple cultivar on pheromone and Pear ester trap efficiency studied as the next tread. In this experiment 32 Delta pheromone traps and 32 Cylinder-shape Pear ester traps impartially mounted on different varieties of apple trees. Artificially reared and marked 24 to 26 h old moths were released at 1 m height from a central point. Among the simple effects the most important explanatory variable for the response variables ?Mn? and ?Fn? moths was sampling dates of moths, while the variety and distance from the releasing point for ?Mn? and the variety and trap height for ?Fn? were the second and third influential variables respectively. Moreover among the nested effects the interaction of distance-height-variety was the most influential one for ?Mn? likewise the interactions of date, release point, direction and trap height with the variety were the most influential for ?Fn?. For the ?Mr? and ?Fr? moths releasing date was the most important influential variable, while the trap type and variety for ?Mr? and variety and trap height for the ?Fr? were the second and third influential variables respectively. Current study revealed that dispersal of the feral and marked-released male and female Codling moths influenced by host cultivars distinctly and decidedly. Meanwhile, quantifying these relationships and propose distinct model for marked and feral male and female moths are the exclusive characteristics of present findings. The next stage of present study related to study of climatic factors on dispersal of Codling moth. In this study, Hohenheim station climatic data were used. Several climatic elements including temperature, relative humidity, precipitation, wind speed in two different heights (2.5 m and 10 m), Day Degree, twilight temperature, wind speed and precipitation were utilized in the analysis. Diversity and high number of variables led us to use AIC method for selecting of appropriate regressors and fitted model. The main regressors that inföuenced the ?Fr? were flight height, ageing, twilight wind speed (2.5 m heights) and precipitation. For the ?Mr? the same regressors plus the distance from the releasing point were the best subset. In the case of the feral moths the flight height, relative humidity, Day Degree, twilight temperature and wind speed were the best subset regressors. Comprehensively we concluded that present study provides new knowledge in basic as well as in applied science. Twilight temperature, rainfall, wind speed and Day Degree impress the distribution of the moths in a superior way than the circadian weather data. This knowledge could mitigate confusion which arises from observations of erratic flight patterns and could lead to fewer treatment decision errors in the future. Also may accelerate and strengthen forecasting programs of this key pest as well as the related management tactics. The combination of mark-release-recapture and diffusion models have been shown to be effective for measuring insect dispersal. We attempted to measure the Codling moth dispersal using traps placed at different distances and heights. Diffusion coefficient calculated for horizontal and vertical dispersal of male and female moths distinctly using direct and indirect methods and resulting models were compared. We fitted the non-linear regression using the iterative process and estimating the parameters accuracy were tested according to the default asymptotic 95 % confidence intervals calculation in non-linear regression. Considering the overall models, suitability of three factors fitted models was more convincible than that of two factors model particularly for male moths. Meanwhile we found great difference in the diffusion coeffcient of direct and indirect methods. Regardless of the model type, the R2 was relatively high in our experiments which evaluate how well the model fits data. We have shown that the diffusion model leads to powerful techniques for the analysis of dispersal data at least for one economically important insect. In conclusion, the present study provides an estimate of population spread by Codling moth using estimated rates of reproduction and dispersal, quantified the association between various key factors and Codling moth movement for the first time using the diffusion model. By including additional parameter to the diffusion model the predictive explanatory potential of this method was improved for dispersal studies at least for a cosmopolitan and critical insect.
Molecular systematics of selected Diadegma species (Hymenoptera: Ichneumonidae: Campoplegine) important in biological control
(2006) Wagener, Barbara; Zebitz, Claus P. W.
The genus Diadegma (Hymenoptera: Ichneumonidae: Campopleginae) represents a large group of parasitoids with 201 species worldwide. Adult Diadegma females parasitise larvae of various lepidopteran species and some species, in particular Diadegma insulare (Cresson) and D. semiclausum (Hellén), have gained economic importance as biological control agents of Plutella xylostella (Linnaeus). A low parasitism rate of <15 % of the parasitoid complex (Diadegma sp., Oomyces sokolowskii (Kurdjumov) and Diaplazon laetatorius (Fabricius)) in unsprayed cabbage and kale fields infested with P. xylostella in eastern and southern Africa was the starting point for the development of a biological control project for P. xylostella which was implemented by the International Centre of Insect Physiology and Ecology (ICIPE), Kenya. One of the objectives of the biocontrol project was to examine the taxonomic status of Diadegma species associated with P. xylostella in eastern and southern Africa and the exotic parasitoid D. semiclausum imported to Kenya from Taiwan (Asian Vegetable Research and Development Centre, AVRDC) by cross breeding experiments and molecular methods. Thus, two different molecular regions, a fragment of the mitochondrial cytochrome c oxidase subunit (COI) and the second internal transcribed spacer (ITS2) of ribosomal DNA were amplified utilising polymerase chain reaction (PCR) and digested afterwards with several restriction enzymes (PCR-Restriction Fragment Length Polymorphism-RFLP). In the due course of the study examinations of several Diadegma species attacking P. xylostella were undertaken with the PCR-RFLP method developed previously for the African Diadegma. This molecular method could solve some taxonomic difficulties of the genus Diadegma. Sequence analyses were used to investigate the phylogenetic relationship of nine Diadegma species (D. blackburni (Cameron), D. insulare, D. leontiniae (Brèthes), D. chrysostictos (Gmelin), D. armillata (Gravenhorst), D. fenestrale (Holmgren), D. mollipla (Holmgren), D. semiclausum, D. rapi (Cameron)) and the phylogenetic relationship of the genus Diadegma within the superfamily Ichneumonoidea. Cross breeding experiments were carried out between two populations of D. mollipla from eastern and southern Africa. No significant differences in the total number of progeny per female and the number of male offspring were obtained, whereas the female progeny showed significant differences. Hybrid females resulting from both reciprocal crosses were reproductively compatible with males of both parental lines, which indicated that no genetic incompatibility was apparent between the two D. mollipla populations. In contrast, crosses between D. mollipla and D. semiclausum resulted only in the occurrence of male offspring, which is typical for unfertilised progeny in Diadegma. The laboratory cultures of D. mollipla and D. semiclausum were highly male biased. Inbreeding, where homozygosity is much higher, is leading to a higher diploid male production. Diploid males can easily be detected by isoenzyme variations as a genetic marker. Heterozygote females/males of D. semiclausum and D. mollipla were identified by phosphoglucomutase (PGM) electrophoretic banding patterns. Crosses between a mother (heterozygote, diploid) and her son (homozygote, haploid) resulted in one diploid male in D. mollipla and none in D. semiclausum. Information about diploid males in D. semiclausum detected with PGM has already been published and different methodologies might be the reason why in D. semiclausum no diploid male was detected. Therefore the present analyses with PGM as molecular marker should be seen as a preliminary study.
Monitoring, mechanisms and management of insecticide resistance and insecticide mode of action in coleopteran pests of winter oilseed rape with special reference to neonicotinoid insecticides under laboratory and applied aspects
(2014) Zimmer, Christoph Thomas; Zebitz, Claus P. W.
Winter oilseed rape, Brassica napus L., has become a vital part of cereal-based crop rotations in Europe. It is attacked by numerous insect pests and their control relies on the intensive use of insecticides (compared to other broad acre crops). The exclusive and continuous use of pyrethroid insecticides for almost twenty years led to an enormous selection pressure and facilitated the development of resistance in oilseed rape pests in Europe. Unsurprising three out of the five major pests of the order Coleoptera are reported to be pyrethroid resistant at present: the pollen beetle, Meligethes aeneus F.; the cabbage stem flea beetle, Psylliodes chrysocephala L. and the cabbage seed weevil, Ceutorhynchus assimilis PAYK.. An adult vial bioassay, which is based on insecticide coated glass vials, was used to monitor the spread and strength of pyrethroid resistance and to determine cross-resistance pattern in pollen beetle and cabbage stem flea beetle. Furthermore, baseline susceptibility towards lambda-cyhalothrin (a widely used pyrethroid) was also established for the cabbage seed weevil. The vial bioassay methodology was adapted to thiacloprid, a neonicotinoid insecticide, to determine baseline susceptibility and to provide a methodology to allow long-term susceptibility monitoring of pollen beetle and cabbage seed weevil. Thiacloprid monitoring revealed that pollen beetle and cabbage seed weevil populations collected across Europe in 2009-2012 and 2012 respectively were highly susceptible to this insecticide class. Metabolism studies using native microsomal preparations as the enzyme source and deltamethrin as substrate revealed metabolism of deltamethrin with 4-OH-deltamethrin being the major metabolite. Metabolite formation in vitro was correlated with the observed pyrethroid resistance level in vivo and was suppressible by PBO. A degenerate PCR approach was used to identify partial P450 gene sequences from pollen beetle. qRT-PCR screening covering a range of pollen beetle populations differing in levels of pyrethroid resistance identified a single P450, CYP6BQ23, as significantly and highly overexpressed (up to ~900-fold) in resistant strains compared to susceptible strains. The expression of CYP6BQ23 was significantly correlated with both the level of resistance and with the rate of deltamethrin metabolism in microsomal preparations of these populations. Recombinant expression of this P450 in an insect cell line demonstrated that it is capable of hydroxylating deltamethrin and tau-fluvalinate. The turnover of these pyrethroids by CYP6BQ23 is in line with the observed moderate cross-resistant phenotype. Molecular modeling suggested a better fit of deltamethrin into the active site of CYP6BQ23 compared to tau-fluvalinate also supporting the biochemical results. The occurrence of target-site resistance was investigated by single nucleotide polymorphism (SNP) analysis of the para-locus encoding the voltage-gated sodium channel (VGSC) in insects. To achieve this goal a partial fragment (domain IIS4-6) encoding an important region of the pyrethroid binding site was PCR amplified and screened for non-synonymous SNPs. One SNP was identified causing a leucine to phenylalanine substitution at amino acid residue number 1014 (Musca domestica L. numbering), well known as knock down resistance (kdr) conferring an absolute cross-resistance to pyrethroids and DDT in various insect species. Sequencing of the very same gene region in the cabbage stem flea beetle also revealed the presence of the L1014F kdr mutation in pyrethroid resistant flea beetle populations, thus explaining the strong cross-resistance pattern observed in vitro. Most mechanistic studies of resistance have focused on elucidating the contribution of particular genes/gene families to pyrethroid resistance. To generate a comprehensive sequence resource and to elucidate global changes in gene regulation related to insecticide resistance in pollen beetle a de novo transcriptome was assembled from sequence pools generated by next-generation sequencing. RNA-sequencing of three pyrethroid resistant and one highly susceptible reference population allowed a global gene expression analysis by short read mapping against the generated transcriptome, as well as a SNP analysis. The implications of these results for resistance management in coleopteran pests in winter oilseed rape and opportunities for future work are discussed.
Morphological and chemical plant properties mediate host plant selection of whiteflies (Hemiptera: Aleyrodidae)
(2021) Stoll, Nina Sara; Zebitz, Claus P. W.
Whiteflies are among the most important pests causing severe damage to numerous cultivated and ornamental plants worldwide. The present dissertation comprises four studies and contributes to the knowledge of the host plant selection process by whiteflies. In the first study, host preferences were determined in dual choice tests for Aleyrodes proletella (L.), Bemisia tabaci (Genn.), and Trialeurodes vaporariorum (Westw.) on several host plants. On the one hand, this study extends the knowledge on the food spectrum of these economically important pests; on the other hand, the results highlight the host adaptation of whiteflies. The second study elucidated potential sources of host plant resistance against A. proletella, B. tabaci, and T. vaporariorum by recording their probing and feeding behaviour on two host plants each using the electrical penetration graph (EPG) method. It is concluded that whiteflies decide upon host plant acceptance by evaluation of multiple plant factors located in epidermal and/or mesophyll tissues of leaves as well as in the phloem sap of plants. Moreover, epicuticular leaf waxes are a key factor in the host selection process of A. proletella. It is hypothesized that constituents of the leaf surface wax act as stimulants promoting leaf penetration and phloem accession. The findings of this study shed light on the whitefly-host adaptation. The goal of the third study was to identify the role of epicuticular leaf waxes of several Brassica cultivars in the host selection process of A. proletella. For this purpose, dual choice tests were carried out on both waxy and dewaxed plant leaves as well as on Parafilm® treated with different leaf wax extracts. Also, life-history traits were monitored on waxy and dewaxed leaves, and the feeding activity of A. proletella was recorded on Parafilm® with and without leaf wax extracts. Scanning electron microscopy (SEM) imaging was used to visualize epicuticular leaf waxes on the plant surface. Finally, it was proved that leaf surface waxes of host plants promote feeding and act as phagostimulants. Although the wax compounds mediating host plant selection remain unknown, these findings offer breeding potential for resistant crop cultivars. In the fourth study, the influence of free phloem amino acids on the host plant selection of T. vaporariorum was investigated. Via liquid chromatography-mass spectrometry (LC-MS), the amino acid profiles in the phloem sap of six vegetable crops varying in their host plant attractiveness were analysed. Subsequently, stepwise multiple regressions of the relative amino acid compositions and the pre-determined host plant preferences were performed. To verify the contribution of single amino acids on host choice, dual choice tests on sucrose media with and without added single amino acids were carried out. Single amino acids play an active role in phagostimulation, whereas some amino acids exert strong inhibitory effects. This indicates that the dominant presence of such amino acids might reduce phloem sap uptake, thus contributing to host plant resistance towards T. vaporariorum. Overall, this research compared the host selection process of three whitefly species to identify their underlying mechanisms. It is hypothesized that the observed host selection strategies are the result of evolutionary adaptations between whiteflies and their host plants. Depending on the occupied ecological niche, species-specific host plant ranges of varying complexity were formed. Accordingly, the host selection process of the more specialised species A. proletella is particularly efficient by consideration of characteristic leaf surface wax stimuli. In contrast, host selection of the extreme generalists B. tabaci and T. vaporariorum is regulated by simple gustatory stimuli in order to take advantage of the host diversity they are offered. The findings of this research provide the basis for new approaches to optimizing breeding programs for whitefly resistant crops.
Overwintering and reproduction biology of Drosophila suzukii Matsumura (Diptera: Drosophilidae)
(2018) Zerulla, Florian Niklas; Zebitz, Claus P. W.
Drosophila suzukii (Matsumura) was introduced to southern Europe and the United States of America in 2008 through fruit imports from Southeast Asia and spread in the following years all over Europe, as well as South and North America. D. suzukii is a polyphagous pest which infests fruits of soft-skinned wild and cultivated plants. In contrast to the well-known D. melanogaster, healthy and ripe fruits are preferred. The infestation is caused by female D. suzukii who damage the fruit skin to deposit eggs underneath with the help of their serrated ovipositor. The feeding of hatching larvae and secondary infections, which can easily penetrate through the damaged fruit, can lead to complete yield losses. A short reproductive period, a large range of host plants and infestation of the fruits, shortly before harvesting makes it extremely difficult to control the pest. Due to comparatively late infestation, the possible period of application during ripening and harvesting is limited. The same applies to the frequency of application of insecticides at this time. Possible residues on the harvested products also carry the risk of rejection of the fruit on the market. Furthermore, an incomplete knowledge of the biology, especially overwintering biology under European environmental conditions makes an effective control of this invasive pest extremely difficult. Therefore, the main research topics are the induction and refraction of the postulated diapause, the detection of any possible hibernation sites and the influence of temperature on the oviposition behaviour of D. suzukii. Based on field experiments it could be shown that successful wintering could probably only take place in forest areas. After freezing, the forest was the only place where D. suzukii could resume its flight activity at warmer temperatures. It has also been confirmed that female flies are more resistant to temperatures below freezing than male flies. Accordingly, after a frost period, hardly any male D. suzukii were caught in bait traps. Similar results have also been obtained in laboratory tests, showing that D. suzukii adapted to low temperatures and shortday conditions had lower temperature preferences and a decreased mortality after changing environmental conditions. It can therefore be assumed that overwintering D. suzukii can spread better in spring due to a lower temperature preference and a higher physical activity under cold environmental conditions than flies without adaptation to winter conditions. Bait traps were also used to determine the developmental status of the ovaries by dissecting the abdomens of weekly captured D. suzukii. This enabled a correlation between microclimatic conditions of individual habitats and the reproductive status of females to be established. In winter, the majority of female D. suzukii had “immature ovaries”, whereas in the summer most females had “mature eggs” in their abdomen. For this reason, it can be assumed that D. suzukii entered a reproductive diapause, which is apparently influenced by winter climatic conditions, nutritional status and the availability of food. In addition, it was found that the developmental status of ovaries correlates positively with oviposition. Laboratory tests were carried out to determine the highest number of egg depositions at 20 °C. Most females with “mature eggs” were also documented under these simulated conditions. We detected that the preferred surface temperature for egg depositing was very similar to the preferred ambient temperature of D. suzukii. Most of the eggs were deposited on fruits with a surface temperature of 22 °C. At this temperature, the highest net reproductive rate and intrinsic rate of population increase was found, too. Temperatures below 15 °C and above 35 °C were not preferred, which represented the thresholds for a successful development of D. suzukii. Temperatures between 10 and 15 °C and shortday conditions were the most important key stimuli for entering the reproductive diapause. Therefore, temperature had a stronger influence on oviposition behaviour than daylength. A complete disruption of diapause occurred at higher temperatures (20 °C) and longday conditions after 72 hours. The data presented in this work on the possibility of adapting D. suzukii to environmental conditions and key temperatures, which influence the development of ovaries and egg deposition, can provide an important contribution to the development of prediction and population dynamics models and can be used for long-term control strategies against D. suzukii. According to current knowledge and observations, overwintering is obviously a critical period for the survival of the populations. Therefore, the characterisation and identification of additional hibernation sites is of great importance. There, a targeted and environmentally friendly control of D. suzukii populations could be particularly efficient.
Pflanzenschutzmittelrückstände im gehöselten Pollen der Honigbiene (Apis mellifera L.) : Auswirkungen einer feldrealistischen Pflanzenschutzmittelmischung auf Stockbienen und den Larvenfuttersaft
(2017) Böhme, Franziska; Zebitz, Claus P. W.
Pesticides are used worldwide and contaminate air, surfaces, soils and the aquifer. Non-target-organisms and non-target-plants may get into contact with pesticides di-rectly via drift or indirectly via run-off, leaching or sowing dust. Due to pollination services and bee products, the honeybee (Apis mellifera L.) is a non-target-organism of major interest for humans. On their flights around the beehive they collect water, pol-len, nectar, honeydew and tree resin. The proteins originating from the pollen are im-portant for nutrition and development of larvae and adults. Pollen is stored and fer-mented inside the hive as beebread and is made of hundreds of pollen loads of differ-ent plants collected over a longer period. Pesticide residue analyses of beebread is a common tool to estimate the contact of honeybees to pesticides in the field. However, such beebread analyses cover a larger time frame and a mixture with uncontaminated pollen will dilute the maximum residue levels of certain plant pollen. Therefore, pesti-cide analysis of bee bread is only an approximate approach to estimate the real pesti-cide exposition. Thus, pollen pellets were collected daily at three distinct sites with differences in agri-cultural intensity in Baden-Württemberg from 2012 - 2016 during the agronomic active season (spring/summer). We wanted to give detailed information on the daily contact to pesticides as well as changing pesticide frequencies and combinations throughout the season. 281 pollen pellet samples, each representing a single day, were analyzed for 282 active ingredients currently used in agricultural practice (publication 1). Huge qualitative and quantitative differences in the pesticide load between the sites were discovered. The meadow site near Göppingen was the least contaminated. In five ob-servation years only 24 different substances were found in 56 % of the samples with concentrations up to 300 µg/kg. The more intensive site in Ertingen is characterized by grains and maize for biogas plants. Only 13 % of the samples were uncontaminated, in the remaining samples 37 substances with maximal concentrations up to 1,500 µg/kg were detected. The site with the highest occurrence of crop protection was close to Heilbronn. Permanent crops such as wine and orchards shape the landscape. The high-est detected concentration was 7,178 µg/kg. All samples were contaminated with up to 58 different substances. During the five years of observation 73 different pesticides were found. Due to admis-sion regulations, there was a high likelihood to find 84 % of these substances in pollen. Twelve substances were found that are either not registered as plant protection prod-ucts or are not supposed to get in contact with bees. This indicates a need for further improvement of seed treatments and increasing awareness of flowering shrubs, field margins and pesticide drift. Concluding from the majority of concentrations and pesti-cides found, we assume no misuse of pesticides by the farmers at our three sites in the observation period, which would lead to direct intoxication. Considering LD50 values, the here detected concentrations are sub-lethal for honeybees. However, at any tested site and in most of the samples a mixture of different pesticides was found. Yet, it is not known, whether there are effects caused by a combination of different pesticides in sub-lethal concentrations when consumed chronically by honeybees. Therefore, we conducted a field experiment with free-flying honeybee colonies (publi-cation 2). Mini-hives containing about 2,500 bees and sister queens were established at the Apicultural State Institute. Queens were confined to an empty frame to receive lar-vae of known age. These bees were intended to feed on pesticides chronically in two crucial life stages. After larvae hatched from the eggs and after adults hatched from the cells they were fed a pollen-honey diet contaminated with a cocktail of twelve dif-ferent active ingredients in field-realistic concentrations. In colonies treated with a pes-ticide mixture, larval weight was higher and acini diameters of the hypopharyngeal glands of nurse bees were smaller than in the untreated control. However, brood termi-nation and adult lifespan did not differ between both groups. Despite feeding a pesti-cide cocktail chronically starting on the first day of larval being, no obvious negative side-effects in worker bees were detected. It raises the question, if nurse bees, which feed on the contaminated pollen-honey diet, produce larval food and feed larvae, serve as a filter system so that larvae would not come into contact with the pesticides. To determine the fate of pesticides originating from the pollen source, we started a queen rearing (publication 3). Frames with 24 h old larvae were hang into queenless free flying mini-hives. At the same time, the colo-nies were fed a pollen-honey diet containing a cocktail of 13 commonly used pesti-cides in high concentrations. The royal jelly (RJ) fed to the larvae by nurse bees was harvested from the queen cells and subjected to a multi-pesticide residue analysis. Sev-en substances were rediscovered in traces (76.5% of all detections were below 1 μg/kg). However, worker larvae older than three days receive a modified jelly, containing pol-len coloring the food yellowish. That is why we were wondering if contaminated pol-len might have a different effect on the food of worker larvae. Queens of free-flying mini hives were caged to receive larvae of known age. The colonies received a pollen-honey diet, contaminated with high concentrations of a pesticide mixture (publication 4, submitted). Worker jelly (WJ) was harvested on four successive days from larval age three to six and subjected to a multi-pesticide residue analysis. Pesticide concentrations increased with larval age and ranged between 2.9 and 871.0 µg/kg for the different substances and age groups. As the increase of substances in the WJ positively corre-lates with the amount of pollen grains counted in the larval food, we were able to show a direct relationship between the administered pollen in the food and the pesticide concentrations. Considering the maximum food uptake rates of a worker larvae, even the highest con-centrations found, would lead solely to sub-lethal amounts. Even for queens, who con-sume RJ not only as larvae but during their whole life would consume only sub-lethal pesticide concentrations. Especially considering the not-field realistic concentrations we chose for our experiments. Probably, the sub-lethal effects found in our first exper-iment are due to the sub-lethal concentrations worker larvae have taken up chronically during their development. Even though we did not detect acute intoxication symptoms and the concentrations in the brood food are sub-lethal, we cannot infer whether there are impairments of fitness or brood success of honeybee colonies in the long term. However, as honeybee colonies are considered as superorganisms, they are able to tol-erate stressors or the loss of individuals. Therefore, the detection of sub-lethal effects on colony-level in the field is difficult. Yet, a vast problem arises with solitary living insects, for example wild bee species, which are more prone to stressors such as pesti-cides. Solitary insects have more restricted flight and collecting areas, get into contact with pesticides in pollen directly as larvae and have almost no buffer capacities.
Prüfung von Citral als Zusatzstoff zu Pheromon zur Bekämpfung des Apfelwicklers Cydia pomonella L. (Lepidoptera, Tortricidae) und des Apfelbaumglasflüglers Synanthedon myopaeformis Borkh. (Lepidoptera, Sesiidae)
(2003) Hapke, Christine; Zebitz, Claus P. W.
In the years 1998 til 2000, a modification of the confusion technique was tested against two pest insects in apple, the Codling moth Cydia pomonella L. and the Apple clearwing Synanthedon myopaeformis Borkh. The respective pheromone was combined with the tentative monoterpene synergist Citral, and applied in the orchard at a density of 125 per hectare as recommended. Laboratory tests were conducted to characterize the effects of Citral mode on individuals of the pests. Field tests with Codling moth revealed no essential differences in the efficiency between the common confusion method with 500 pheromondispensers per hectare and the new technology with Citral (125 dispensers/ha) as expressed in numbers of male caught in pheromone traps or in percent fruit damage under low pest pressure. Both methods failed under high pest pressure. Weighing the dispensers weekly followed up the release of Citral and the pheromone. In semi-field tests in large cages (2 m  2 m  2 m) pest population density seemed to have no impact on control success. In small cages (30 cm height, 30 cm ) the copulation rate in the pheromone plot was significantly lesser than in the Citral-treated atmosphere and in the untreated control plot. Using a laboratory wind tunnel undiluted and 10-1 diluted Citral resulted in a significant decrease of the attractiveness of pheromone. After 24 hours this effect diminished. Half-life of released Citral was approximately two hours. After four hours about 100 µg/h 10-1 diluted Citral was still released into the tunnel. Electroantennogrammes of both, male and female antennae of C. pomonella showed a strong reaction to Citral. The reaction of the antennas to pheromone was strongly overlaid by Citral. In laboratory tests in a closed system, copulation of the moths could be prevented starting from a Citral concentration of 2000 mg/l. Male moths, previously exposed to Citral for 24 h, were not able to copulate with mature, unmated females. Citral-exposed females (24 h exposure time), however, were successfully mated by mature untretaed males. Any impact of Citral in concentrations up to 1,500 mg/l on oviposition could not be proven. Furthermore, first larvae of the Codling moth were not prevented to penetrate into an apple with up to 5,000 mg/l Citral. Field tests with the Apple clearwing proved significantly lesser pheromone trap catches in the Citral-treated plots than in the control plots on five alternatively six test orchards. The plots with 500 and 250 pheromone dispensers per hectare also exerted rates of confusion of up to 100 %. In a plot with 250 Citral dispensers per hectare, an effect of confusion could not be observed. Catches in lure pots showed no difference in the amount of mated or unmated females between plots. The amount of mated females in all plots was much higher than those of the unmated. The amount of fresh frass in treated and untreated plots was too small for proving a success of control. The quantitative preparation of the larvae in coincidentally selected trees on a plant showed a significant difference between the Citral-treated plot and the untreated control plot. However this difference is based only on a reduced number of larvae up to 7 mm body length. Tests with S. myopaeformis in a laboratory wind tunnel were not successful, because the attractiveness of the traps baited with pheromone were not very high. Investigating the environmental conditions for a successful copulation of S. myopaeformis the light intensity did not prove to play the major role. Temperature and wind velocity seem to possess a substantial meaning, dominating light. The copulation rate in small cages (30 cm height, 30 cm ) generally hardly reached 50 % and was very small thereby. In the laboratory moths of the apple clearwing could not be brought to copulation. Synergisation of pheromones with Citral seem to be not recommendable under practical conditions.
Resistenz von Hopfen, Humulus lupulus L., gegen die Hopfenblattlaus, Phorodon humuli (Schrank)
(2010) Kryvynets, Oleg; Zebitz, Claus P. W.
Non-chemical methods controlling the damson-hop aphid, Phorodon humuli (Schrank) have recently gained importance, due to its great economical relevance and increasing problems with its chemical control. Breeding for the classic 'Genetically controlled resistance', where the plant exerts negative influence on the pest's behaviour during feeding, in this case appears as the only promising method because so far no other efficient biological control methods are available. In order to analyse the host-parasite relationship between hop and damson-hop aphid, and to provide a reliable, standardised screening method based on line-specific host selection behaviour, 1. the composition of the aphid's food, 2. hardness of hop tissue, 3. host selection behaviour and 4. parameters of aphid growth and development were investigated. In the apoplast (Intercellular washing fluid) of leaves and cones from all hop lines resveratrol was found, which also indicates an accumulation of its glycosidic form in the plant tissue. In contrast, no resveratrol could be found in samples of non-transgenic hop. An analysis for bitter acids detected alpha- and beta-acids in the cones only, not however in the intercellular space of the leaves. In a comparative study of plant tissues the contents of lupulones in leaf extracts from transgenic plants (except Tk160 and Tk424) was lower, the contents of humulones higher compared with those from non-transgenic plants. Generally leaf extracts showed higher contents of alpha- than of beta-acids. Resveratrol was not found in any of the leaf- or cone-extracts. Tissue hardness differed between transgenic and non-transgenic plants as well as between those from the glasshouse and from open land. In the field-grown plants it was definitely higher. Leaves of transgenic lines were harder than those of non-transgenic ones. This difference was pronounced particularly in young leaves. Significant differences were observed among parameters of aphid growth and development. The individual transgenic lines exert significantly different influence on P. humuli in respect of relative growth rate of individuals, rate of population increase and fecundity. There was no significant difference between the variants regarding the parameters rDS-value, life span and number of embryos. Host selection behaviour was different on transgenic versus non-transgenic plants. On leaves of transgenic plants a slowing down of food intake from the phloem and an extension of water intake from the xylem were observed. On the cones no similar effect ? general reduction or extension of intake from phloem or xylem in comparison to non-transgenic plants ? could be ascertained. Generally a strong decrease in food intake from the phloem of cones compared to that of the leaves was observed, caused by frequent phases of aphid inactivity on cones. Aphid behaviour on artificial diets was definitely influenced by different concentrations of bitter acids and resveratrol. A gradual increase in bitter acid concentration first prolonged or raised some EPG-parameters and then shortened or reduced them subsequently. This means that the aphids first reacted negatively, from a certain concentration of bitter acids on, however, positively to these substances. A raise in resveratrol concentrations led in the whole course either to a notable increase or decrease of values for the individual EPG-parameters. This suggests a xenobiotic resistance effected by this substance. Correlations between the experimental data showed the following dependencies: The humulones and lupulones found in intercellular washing fluid and in tissue extracts influence EPG-parameters that indicate factors located in the mesophyll. The duration of those phases of the penetration that take place in the intercellular space is reduced with increasing concentrations of humulones and lupulones. Food quality and quantity in plants from the glasshouse had no negative effects on the damson-hop aphid. On field-grown plants different effects of alpha- and beta-acids in the extracts on the aphids were ascertained. The contents of lupulones in cone- and leaf-extracts exerted a more inhibiting, the humulones a more promotional effect on the aphids during feeding. As with the overall contents of humulone and lupulone a different influence of individual bitter acids on aphid behaviour was recognisable in EPG-parameters. On cones the strong behaviour modification by the examined substances took effect on the mesophyll level and in the phloem. Positive correlations between the adult weight of the aphids as well as the amount of offspring per life span per insect and the bitter acid contents indicate an influence in favour of the insect. Negative correlations between the rm -value and the bitter acid contents, however, show an influence on the aphids in favour of the plant. Higher bitter acid concentrations reduce the development rate of aphid populations. Notable differences between transgenic and non-transgenic plants as well as varying effects of examined substances on the aphids, partly favourable for the plant, partly favourable for the pest, were found. These differences were partially clarified by comparing the effects of the substances when administered with artificial diets. The exact mode of action of resveratrol and its derivatives in transgenic hop lines on the damson-hop aphid requires further examination. A direct toxic effect on the aphids is very probable. As a conclusion from the clustering by examined parameters the transgenic hop line Tk424 can be designated as optimal.
Strategien zur Regulierung des Fruchtschalenwicklers Adoxophyes orana F.v.R. (Lepidoptera: Tortricidae) mit Kombinationen des Neem-Präparates NeemAzal-T/S und Entomopathogenen
(2002) Kumpmann, Sophia Katharina; Zebitz, Claus P. W.
The summer fruit tortrix moth Adoxophyes orana F.v.R. is known as a serious pest in pome fruits in Central Europe. According the new laws on plant protection in Germany, only few registered products are left which may be used in organic and conventional farming at present. The registered products used in organic farming base on the specific Adoxophyes orana granulovirus (AoGV; tradename: Capex) and Bacillus thuringiensis (Bt). The application of Capex in order to reduce high population densities led to various results, some of which proved to be insufficient. The results of Bt application were not satisfying, either. The application of 3 l/ha NeemAzal-T/S, a product based on Neem (Azadirachta indica A. Juss.) -extracts and plant oil, for aphid control in apple orchards shows promising side effects on Adoxophyes orana with a mortality rate of about 60 - 70%. However, the efficacy of the recommended dose of 3 l/ha at red bud stage is not high enough to obtain a satisfying control of A. orana in orchards with medium and high population densities. A possible positive aspect may be the long-term effect upon the population of A. orana following the application of both, Capex or NeemAzal-T/S. Until now, however, long-term effects have not been considered in control strategies. Thus, this study aimed towards to take advantage of these side effects of the application of NeemAzal-T/S in combination strategies with Bacillus thuringiensis or Capex for efficient and economically interesting control of this pest. Field and laboratory tests were carried out to test different strategies of combinations including short-term and long-term effects of the products. In addition, the aim of some laboratory trials was to test appropriate Bt-products and further additives for A. orana regulation. Combination of NeemAzal-T/S and a Bt-product In laboratory trials and field tests, different concentrations of NeemAzal-T/S and Bt were combined and sprayed at the same time to assess the effects of this strategy on the larvae of A. orana. This combination showed neither additive nor synergistic effects, no matter the concentration used. A successive strategy with a first application of NeemAzal-T/S either with or without adding 0,4 kg/ha Bt and with a second application of 0.6 ? 1.0 kg/ha Bt lead to high efficacy. Application of NeemAzal-T/S ? in doses of 2 l/ha or 3 l/ha in the first treatment ? turned out to be an important factor to achieve a good result. The addition of 0.4 kg/ha Bt to the first application did neither show a better nor a worse result. Obviously, this successive combination strategy leads to lower negative influence of the feeding inhibition, which seems to be partly responsible for the negative effects on A. orana when both products were applied at the same time. Combination of NeemAzal-T/S and Capex In organic farming, Capex at 100 ml/ha is applied two times in spring. Aim of the following tests was to minimise the risk of failure of a treatment with Capex by taking advantage of the positive side effects of the application of NeemAzal-T/S and to find out whether a reduction of the amount of Capex may be possible in this combination. In laboratory trials, no synergistic effects of a combined application of both products could be observed. In fields, Capex applications leading to 50 ? 60 % efficiency could be raised to 81 ? 94% by adding of NeemAzal-T/S. When Capex applications led to a larval mortality rate of 90% or more, the addition of NeemAzal-T/S showed no effects. Furthermore, the long-term effects of the combination of NeemAzal-T/S and Capex were taken into account. One trial showed that the increased efficiency of the combination was higher when considering also the number of larvae of the subsequent two generations, than assessing the larval mortality rate in the treated generation only. This leads to the conclusion that either the long-term effect of NeemAzal-T/S alone or of both products together reduces the population density of A. orana in the generations following the treatment. Long-term effects of Capex Aim of this part of the studies was to estimate whether an application of a small amount of Capex in summer in addition to the usual spraying in spring leads to a higher infection potential in the orchard. With the additional treatment, the rate of infected larvae in summer could be increased from 8% to 22%, and the amout of damaged fruits from 0.2 % to 0.6%. But both infestation rates were very low and, thus, too weak to support any interpretation. Thus, the additional treatment in the summer turned out to be of economical advantage. The repeated use of this virus product in various concentrations and against various generations of A. orana seems to be a very promising strategy. It remains to further research and long-term studies to elucidate the most efficient sequence, amount and dates of application of the virus to obtain maximum control of A. orana.
The host parasite relation of the parasitic mite Varroa destructor (Anderson and Trueman) and the honeybee races A. m. syriaca (Skorikov) and A. m. carnica (Pollmann) in Jordan.
(2006) Al-Attal, Yehya Zaki Khalid; Zebitz, Claus P. W.
Since the honeybee mite Varroa destructor (Anderson and Trueman) succeeded to parasitize the Western honeybee Apis mellifera L. and accept this species as a new host it became the most serious threat to Apiculture worldwide. The very few stable relations between Varroa mites and the new host are either associated with honeybees of African origin, or with tropical and sub-tropical climates. This balanced relations seems to be due to reduced fertility of the female mites in worker brood cells, a shorter post-capping period of the worker brood and a set of highly differentiated active defense traits of the host bees. In this work I investigated several aspects of the host parasite relation between the honeybee and the Varroa mites in Jordan. The endemic honeybee race of Jordan is A. m. syriaca Skorikov, which join African and European bee traits. The Jordanian beekeepers use this ?local? bee as well as its hybrids with imported European bees. Therefore, Jordan provides the possibility to prove the influence of different honeybee races and different climatic conditions on this host-parasite system. For a better direct comparison, I evaluated the host-parasite relation of two honeybee races at the same study site: the ?local? honeybee (A. m. syriaca) and the imported ?carnica? honeybee (A.m. carnica Pollmann), which is susceptible to Varroa infestation under Central Europe conditions.To assess the current status of Varroa mite in Jordan, we surveyed the infestation rates of in capped brood cells and on adult worker bees in 180 honeybee colonies at six locations. All colonies were kept untreated for at least 8 month. The results revealed high infestation rates, which exceed, in part, the thresholds for colony damages. No significant differences between honeybee races or climatic condition were visible. The population dynamics of the host and its parasite represents the most important parameter of the honeybee-Varroa relation and was described in the ?local? and the ?carnica? (imported from Hohenheim) honeybees at Baqa (dry Mediterranean climate) and Yadodeh (wet Mediterranean climate) for a one-year period. In all colonies the number of adult bees and brood cells were evaluated every three weeks by the ?Liebefeld? method. During all evaluations, samples of adult bees and capped brood of all colonies were analyzed to determine Varroa infestation rates. The population dynamics of the honeybee colonies revealed a significantly higher population density of the ?local? honeybee race compared to the ?carnica? colonies. The average number of adult worker bees was 8,368 ± 2,724 in the ?local? colonies and 6,447 ± 2,338 in the ?carnica? colonies, while the average number of capped worker brood cells was 9,164 ± 3,336 in the ?local? and 7,628 ± 3,166 in the ?carnica? colonies. Compared to colonies in Central Europe, my results indicate a surprisingly shorter life span of adult worker bees. The corresponding population dynamics of Varroa mites revealed an exponential growth phase till the maximum infestation and a decreasing phase until the beginning of the next season. The maximum Varroa population density ranged between 2,614 ± 2,190 mites in the ?carnica? colonies and 4,397 ± 2,746 mites in the ?local? colonies. Using an exponential function, growth rate = eb, the average exponential growth rate of Varroa population per three weeks interval ranged between 1.33 and 1.46 and was significantly different between both locations. The subsequent decrease in the mite population was two folds higher than the decrease in the effective bee population (adult bees plus capped worker brood cells together). Therefore, a higher mortality rate of the parasites or its host activity must contribute to the observed drastic decrease of the Varroa population. No significant race-specific differences in the infestation rates could be observed. However, the mortality rate was higher in the ?carnica? colonies (? 40%) compared the local colonies (? 10%). This indicates a general higher fitness of the ?local? colonies independent from Varroa infestation rates. As a threshold for the survival of honeybee colonies, maximum infestation rates of 20% in adult worker bees and 40% in capped worker brood were determined. The evaluated resistance mechanisms, which are considered to contribute to stable host-parasite relations, did not reveal any pre-adaptation of the ?local? honeybee to Varroa mite. Neither in the fertility of female mites nor in the reproductive rate significant differences between the local and the ?carnica? honey bee race could be detected. The post-capping period of the worker brood was nearly the same in both bee races and it corresponds to data from Central Europe. Also no significant difference could be revealed in the daily mite mortality between both races, which ranged between 0.8% and 1.5% of the total mite population in the colonies. Nevertheless, in few individual ?local? colonies, the mite mortality comprises a surprisingly high percentage of the total estimated number of the phoretic mites within the colonies. By RFLP of the CO-I unit, only the V. destructor Korean haplotype was detected in all examined mite samples from Jordan. Additionally, mite genotyping based on the sequences of two genetic markers shows very low genetic variability among different mite populations, which confirm recent publications and makes the hypothesis that differences in mite virulence could be responsible for a stable host parasite relationship, less probable. Conclusions ? The ?local? honeybee of Jordan is not more resistant to Varrosis compared to the susceptible European honeybee races. ? The Mediterranean climate has no significant inhibition effect on Varroa population dynamics. ? Varroa infested ?local? honey bee colonies revealed a significant higher survival rate than imported ?carnica? colonies under the same conditions. ? Variation in the mite infectivity between different V. destructor population is less probable.
The role of pollen as alternative food for predatory mites (Acari: Phytoseiidae)
(2018) Schreiber, Irina; Zebitz, Claus P. W.
Predatory mites of the family Phytoseiidae (order Acari) are important biological control agents of various greenhouse pests. Their successful establishment in greenhouses depends on abiotic and biotic factors, and on different adaptation levels of the different mite species, which must be considered before practical implementation. In this study, the suitability and effect of pollen as alternative food was assessed for the predato-ry mites A. swirskii, A. limonicus, and A. cucumeris (Acari, Phytoseiidae). Besides lifetable and demographic parameters, body weight and size was included into the descriptive parameters, which has not been done before to obtain more detailed information on pollen quality for these mite species. In the first study (Goleva and Zebitz 2013), the suitability of pollen of 21 plant species as alternative food for A. swirskii was tested. Preimaginal mortality and developmental time have been assessed, followed by a life-table analysis of the emerged adults and a calculation of demographic parameters. Amblyseius swirskii was able to feed on 18 pollens, but the nutritional properties of the pollen differently affected mite performance. Pollen of Lilium martagon and Hippeastrum sp. were found to be toxic for the mites, probably due to secondary plant compounds in this pollen. Amblyseius swirskii was absolutely not adapted to feed on Hibiscus syriacus because of the external morphology of pollen grains, leading also to 100 % preimaginal mortality. The best pollen resulting in superior mite performance in all parameters tested were: Aesculus hippocastanum, Crocus vernus, Echinocereus sp. and Paulownia tomentosa. No or low mortality was observed when mites fed on other pollen tested. Developmental time, adult longevity, and reproduction parameters, were significantly affected, probably because of differences in pollen nutrient or non-toxic secondary compound composition. Commercial bee pollen was of very poor quality for the mites leading to low egg production, which excludes this pollen for practical use. Pollen of Helianthus annuus, Corylus avellana and a Poaceae-mix were of inferior quality, causing high mortality rates, low egg production and short adult longevity. For practical implementation in greenhouses, pollen of Ricinus communis, Zea mays, A. hippocastanum and Betula pendula pollen appeared suitable to improve predatory mite performance, either provided by banker plants or in form of dispersible pollen. The objective of the second study (Ranabhat et al. 2014) was to assess the suitability of seven pollen (castor bean, tulip, apple, Christmas cactus, horse-chestnut, maize, and birch) for Neoseiulus cucumeris (Acari: Phytoseiidae), and to scrutinize potential effects of these pollen on reproduction and life history parameters of this mite. Neoseiulus cucumeris accepted six pollen sources as alternative food, pollen of castor bean plants, however, caused 100 % mortality. Highest fecundity was observed when feeding on pollen of tulip and horse chestnut, resulting in the shortest preimaginal development compared with all pollen tested. Pollen of birch, tulip, maize, and apple had a positive effect on longevity, whereas pollen of horse-chestnut and Christmas cactus was significantly inferior. Our study suggests that birch, tulip, horse-chestnut, apple, and maize pollen may serve as alter-native food in the field, and birch and maize pollen have a good potential in practical use as banker plants or dusts in the greenhouse to guarantee mite establishment in periods of prey scar-city. The aim of the third study (Goleva et al. 2014) was to investigate the role of pollen of differing quality (tested previously in first study (Goleva and Zebitz 2013) on size and weight of A. swirskii. These parameters were considered from the physical aspect of predator-prey relations because predatory mites are not able to conquer prey individuals bigger than themselves and any deviation from normal size may negatively affect predation success. Biomass and body size of freshly emerged, 1, 3, and 30 days old adult A. swirskii continuously reared on pollen of B. pendula, H. annuus, P. tomentosa, and Zea mays revealed, regardless of pollen source, that females were bigger than males. Both parameters weight and size were affected by pollen tested. Females fed on pollen of P. tomentosa and Z. mays were significantly bigger than on B. pendula or H. annuus pollen. Increase of female biomass was observed until the adult age of 3 days, remaining constant or slightly decreased until the age of 30 days. This can be explained by particularly high nutritional requirements of females for egg production especially in the beginning of their repro-duction period. Males also reached their weight maximum at day 3 of adult life, then decreasing until day 30. Congruent with biomass, adult body length and width differed significantly depending on sex and age showing females bigger than males and 30 day old adults bigger than 1 day old adults irrespective of the pollen fed. While sunflower pollen was of poor quality for A. swirskii, causing small size and low weight of both sexes, pollen of P. tomentosa was significantly superior in both parameters. No reasonable correlation was found between body length and width, but body weight was significantly correlated with body length in females whereas there was no correlation at all in males. In a fourth study (Goleva et al. 2015), adult body weight of the generalist mites A. swirskii, A. limonicus, and N. cucumeris reared on 22, 12, and 6 pollen species, respectively, was assessed. In addition, A. swirskii and A. limonicus were reared on codling moth (Cydia pomonella) eggs.In addition, A. swirskii and A. limonicus were reared on codling moth (Cydia pomonella) eggs. In addition, A. swirskii and A. limonicus were reared on codling moth (Cydia pomonella) eggs.In addition, A. swirskii and A. limonicus were reared on codling moth (Cydia pomonella) eggs. In all mite species, female body weight was higher than that of males.Nutritional quality of pollen was neither consistent among the mite species nor among sex, revealing superior quality of Quercus macranthera pollen for females of A. swirskii and T. gesneriana pollen for males, Alnus incana pollen for females of A. limonicus and Ae. Hippocastanum pollen for males, and Ae. Hippocastanum pollen for both sexes of N. cucumeris. Pollen affected predatory mite species in our studies in various ways. Besides lifetable parame-ters, pollen also affected adult weight and size of predatory mites and these parameters should therefore be considered additionally in future studies to obtain more exhaustive information on nutritional biology and physiology of predatory mites. The differences in the parameters assessed and the mite species performance may be explained by different adaptations of mite species to pollen compounds. Knowledge in the chemical composition of pollen, however, particularly the nutritive substances, is poor or even lacking. Any correlation of performance parameters with nutrients is more or less theoretical unless the pollen constituents are known. Even then, nutritional physiology of predatory mites and their adaptation to various food sources must be improved and include mite’s enzymatic activity to metabolize secondary plant compounds in pollen. The results presented in this thesis open the door to future research on mite nutritional biology.
Untersuchungen zur Bedeutung und Lebensweise phytophager Thripse (Insecta, Thysanoptera) als Verursacher von Austriebsstörungen an Reben als Grundlage zur Entwicklung umweltschonender Bekämpfungskonzepte
(2006) Wipfler, Rosi; Zebitz, Claus P. W.
Aim of this study was to gain basic knowledge of the biology of thrips pest species on grapevine. The results should provide the basics to develop environmentally compatible protection strategies. From 2002 to 2004, a monitoring of thrips infested vineyards was done in the vine growing region Palatinate. Thrips population dynamics and level of infestation were investigated in different newly planted vineyards and nurseries, as well as the damage caused by thrips. To answer the question, how and where thrips hibernate in vineyards, different collection techniques were tested to detect thrips in the soil and underneath the bark of vines. During the vegetation period, the flight activity of thrips was monitored in different vineyards and nurseries. Thrips species of vineyards, surrounding crops and shrubberies were compared to reveal possible ways of infestation by thrips on grapevine. Different insecticides were tested to control adult thrips and larvae in the field. Considering the collected thrips species, most striking result was the dominant abundance of the onion thrips, Thrips tabaci Lindeman, which caused most of the damage. The expected grapvine thrips Drepanothrips reuteri Uzel was of minor importance. Preferences for different grapevine varieties could not be found. Infestation mainly appeared in nurseries and newly planted vineyards. 30 different thrips species could be detected on grapevine. The results on level of infestation and phenology corresponded mostly with the literature data on D. reuteri. In the investigated vineyards, infestation was only detected in spring. In three years of investigation, infestation rates decreased from the middle of June onwards. The reason was mainly a migration of the polyphagous T. tabaci to other host plants. The detailed description and documentation of thrips infestation symptoms resulted in additions to already known symptoms. It was also possible to make further differentiations to infestation symptoms not caused by thrips. During the investigations it could be proved that different thrips species overwinter underneath the bark of vines and in the soil of vineyards. Therefore, thrips can rapidly infest vines in the following spring. Field experiments with yellow water traps showed that airborne adult thrips and thrips that actively migrate from surrounding crops are of major importance for the infestation of grapevines. Nurseries showed an increased risk of infestation, because they are usually located outside the grapevine areas and are surrounded by other crops. In this study it was not possible to gain any hint that thrips are transferred by grafted vine cuttings. The influence of shrubberies on thrips species in vineyards was of minor importance but needs further studying. It would also be of interest to investigate the influence of different culture techniques on the level of infestation and the phenology of thrips in vineyards. The insecticidal compounds spinosad, abamectin and imidacloprid proved to be effective to control thrips in the field. For newly planted vineyards, two treatments are recommended in spring: first against adult thrips at the beginning of May, and the second against the hatched larvae 14 to 21 days later. Treatment is necessary at levels of infestation of more than one thrips per shoot at the grapevine developmental stage BBCH 09 to 13, and with more than one thrips per leave at BBCH 14 to 17, respectively. Preventive treatment is recommended 1. for newly planted nurseries, if there is an increased risk of infestation because of surrounding crops with detected thrips infestation, and 2. at the beginning of budding for newly planted vineyards and one year old vineyards, especially if there was thrips infestation in the previous year and if predatory mites are absent. Control experiments in the laboratory could not be done, because it was not possible to establish a thrips colony to supply enough thrips material. The results of this study contributed to the approval of the compounds imidacloprid and abamectin for minor uses to control thrips on grapevine in 2006.
Vermehrungs- und Schadpotential der Grünen Gurkenlaus (Aphis gossypii Glover) an Gewächshausgurke (Cucumis sativus L.)
(2003) Bünger, Isa Brigitte Annemarie; Zebitz, Claus P. W.
The aim of this work was to collect basic data for the development of a model which could simulate the injury of greenhouse cucumbers caused by Aphis gossypii G.. This work mainly deals with two aspects: first it is the population dynamics of A. gossypii influenced by infestation density (initial infestation 2-10 individuals per plant) and host plant quality (age) and second it is the quantitative and qualitative assessment of damage by investigation of growth, yield, and chemical composition of the cucumber plants. The investigation took place under controlled, semicontrolld and practical conditions.