Browsing by Subject "Parasitoid"

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Elucidating the megadiversity of Chalcidoidea (Hymenoptera) with a multi-taxonomic approach
(2022) Haas, Michael; Krogmann, Lars
With over 22,500 described and up to 500,000 estimated species, the jewel wasps (Chalcidoidea: Hymenoptera) are among the most species-rich insect lineages. Their evolutionary success is tightly linked to their parasitoid biology, having evolved to utilize a wide array of different arthropod hosts. Additionally, secondary phytophagy evolved several times within this superfamily. Although new approaches are employed in integrative taxonomic research, progress to decipher the megadiversity of this taxon, including their evolution, is still limited. With this work, the diversity of the superfamily is studied at two evolutionary key points in time. The evolutionary origin of Chalcidoidea is investigated in the Cretaceous and the resulting diversity since then is examined in the present. Different systematic levels will be elucidated with the help of integrative taxonomic methods. In the first chapter, the fossil origins of jewel wasps are addressed, around the middle of the Cretaceous period 110 million years ago. The morphology of a putative early chalcidoid specimen is studied, as it is highly informative for chalcidoid evolution due to its age. Based on those results, its phylogenetic placement is critically examined. The specimen is assumed to be one of the oldest described chalcidoid fossils, Parviformosus wohlrabeae Barling et al., 2013. It is a key fossil because of its age and putative assignment to the polyphyletic family Pteromalidae and could therefore be a valuable voucher for dating modern phylogenies. A precise redescription of the fossil was conducted and its morphology and phylogenetic position was discussed. No synapomorphic characters could be identified, warranting an inclusion in an already established chalcidoid family. In fact, none of the autapomorphies for Chalcidoidea could be recognized, necessitating a revised systematic placement in the Proctotrupomorpha. In the second chapter, several fossils in amber are described that grant insights in the early evolution of Chalcidoidea and the morphological diversity of Cretaceous lineages. Morphological characters are studied to answer the question of plesiomorphic character states in Chalcidoidea, aiding to understand their early evolution. The phylogenetic placement of these fossils is discussed, to provide hypotheses on the diversification of the superfamily, which so far has only few fossil representatives described from this time. Four fossils are made scientifically available that were found in 99 million year old Burmese amber. Those specimens are described in a new, extinct family, the Diversinitidae. This family exhibits a unique combination of plesiomorphic characters, not present in any other chalcidoid taxon, but lacks apomorphic characters. In total, three new genera and three new species are delimited and described. Phylogenetically relevant characters like the fully developed funicular segments, possessing multiporous plate sensilla, or the peg like cerci that improve our understanding of the early evolution of Chalcidoidea, are discussed based on the newly established family. A phylogenetic analysis based on morphological characters was performed. This analysis supported the monophyly of Diversinitidae, but left its exact systematic position within Chalcidoidea open. In the third chapter the focus shifts from the early evolution of Chalcidoidea towards the extant fauna, representing the diversity evolved since the Cretaceous. Exemplary, in the speciose family Pteromalidae the unknown diversity is examined to better understand the undiscovered species richness of parasitoid wasps. DNA barcoding is used to record and help identify previously unknown genera and species in Germany. Compared to the already known pteromalid fauna, 17 genera and 41 species are added as new records for Germany and the males of two species are described anew. The identified DNA barcodes were made available to enable the genetic identification of those species that have a high potential as indicators for nature conservation efforts due to their high host specificity. In the fourth chapter, the pertinent problem of cryptic diversity in Chalcidoidea is investigated. Via an extensive integrative taxonomic approach, the morphological species hypothesis is tested for one of the most abundant pteromalid species in Europe, Spintherus dubius. In this example, the benefit of combining different methods for species discovery and delimitation is highlighted. Genetic analyses of S. dubius reveal discrepancies between the morphological species concept and molecular data, indicating two potential species instead of one. The usage of an advanced morphological method, the multivariate ratio analysis, results in a confirmation of the molecular results, also exposing distinctive morphological characters per taxonomic unit. The examination of the host spectrum through rearing experiments further substantiates these findings, by revealing different host parasitoid affiliations. Altogether, this thesis showed that it is necessary to combine methods and examine different evolutionary points in time, to better understand the diversity of parasitoid lineages. Fossil taxa are important study subjects to examine the character evolution of any taxon, laying the base for phylogenetic research. The study of Diversinitidae highlights the plasticity of character states in Chalcidoidea, also providing evidence for plesiomorphic states. Their encompassing description and the redescription of P. wohlrabeae allow their incorporation into phylogenetic studies, to serve as solid anchor points in dating lineages and morphological evolution on the way towards extant diversity. Examining the extant fauna of Pteromalidae revealed the amount of diversity of species, for which the biology is often unknown. It is shown that molecular methods aid in the discovery of this diversity, opening possibilities for further research. It is affirmed that hidden diversity is even pertinent in abundant, well known species, with S. dubius being an example of cryptic diversity unveiled by integrative taxonomy.
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.
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.
Trophic level and specialization moderate effects of habitat loss and landscape diversity on cavity‐nesting bees, wasps and their parasitoids
(2024) Klaus, Felix; Tscharntke, Teja; Grass, Ingo
1. Habitat loss is a primary driver of biodiversity decline, but differences in species responses to habitat loss from local to landscape scales are poorly understood. 2. Trophic level, food and habitat specialization have been suggested to be important predictors of species responses to habitat loss, landscape diversity and landscape scale. 3. Using cavity-nesting communities of bees, wasps and their parasitoids on calcareous grasslands as a model system allowed us to compare responses of species differing regarding their trophic level, and degree of specialization on habitat and food. 4. We found that species from higher trophic levels experienced semi-natural habitat at larger spatial scales than those of lower trophic levels, but only, when they were generalists (abundance of bees, 150 m radius, vs. wasps feeding on herbivores, 450 m radius), not specialists (bees, 150 m, vs. bee parasitoids, 150 m). 5. Parasitoids, which are typically more specialized regarding their food resources (hosts), compared to predators such as predatory wasps, responded to habitat loss at the same spatial scales as their hosts, suggesting strong bottom-up effects of resource availability, that is, host availability driving parasitoid abundance. 6. Bees were mostly habitat specialists of calcareous grasslands and mainly driven by local habitat loss, whereas wasps as habitat generalists were mostly affected by landscape diversity. 7. Our study highlights the need to consider the different spatial scales contingent on trophic level and specialization of target species groups, maintaining or restoring both local habitat and landscape diversity, as this is needed for their successful conservation.