Browsing by Subject "Entomopathogene Pilze"

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Otiorhynchus spp. (Coleoptera: Curculionidae) as pests in horticulture: genetics and management options with entomopathogenic fungi
(2012) Hirsch, Jacqueline; Reineke, Annette
Worldwide, weevils of the genus Otiorhynchus (Coleoptera: Curculionidae) cause damage with detrimental economic effects to many horticultural crops due to the root feeding of their larvae as well as foliage feeding of their adults. Aside from the black vine weevil Otiorhynchus sulcatus, which is the best-known pest within this genus, numerous other Otiorhynchus species have been increasingly recognized as pests in recent years. Nocturnal adult weevils and soil-inhibiting larvae are in principle difficult to control with biological or chemical plant protection products. In addition, each Otiorhynchus species shows a different phenology or may have a varying susceptibility towards plant protection products. Therefore, the exact species identification of the respective weevil pest is a prerequisite for the development of efficient control strategies. While adult weevils can be distinguished by phenotypical characteristics, the determination of Otiorhynchus eggs, larvae and pupae, only on the basis of morphological features, is nearly impossible. For that reason, a molecular diagnostic method, which allows the species determination of 16 Otiorhynchus and eight other weevil species, independent of their developmental stage, was developed. This diagnostic method might be used in future for fast and cost-efficient species identification of weevils in plant protection. The application of entomopathogenic nematodes is a well established method for biological control of O. sulcatus larvae. Another biocontrol strategy is the application of entomopathogenic fungi. So far, both entomopathogenic fungi and nematodes have been used mainly against the black vine weevil. As less is known about the effectiveness of entomopathogenic fungi against different Otiorhynchus species, the present thesis analysed the efficacy of the entomopathogenic fungi Beauveria bassiana, Isaria fumosorosea and Metarhizium anisopliae (formulated in the commercially available products Naturalis®, PreFeRal® WG and GranMet-P®, respectively) against different developmental stages of several Otiorhynchus species under laboratory conditions. Infection experiments revealed that different species of adult Otiorhynchus weevils show a different susceptibility to the analysed entomopathogenic fungi. In addition, a method to quantify the efficacy of entomopathogenic fungi against adult Otiorhynchus spp. under field conditions was developed. Worldwide, entomopathogenic fungi, in particular the species B. bassiana, are used for biological insect pest control. They are either incorporated into the potting media at the time of planting or applied directly onto the plant or onto the surface of the soil. While the effect of entomopathogenic fungi against insects has been well studied, little is known so far about their fate, spread and influence on the naturally occurring soil fungi. As decomposers of dead organic material or as mycorrhizal symbionts of plants, fungi play an important role in the terrestrial ecosystem. New insights into the fate, spread and interactions of entomopathogenic fungi and soil-inhabiting microorganisms could therefore provide important information for proper risk assessment of plant protection products which are based on entomopathogenic fungi. For this reason, the influence of the entomopathogenic fungus B. bassiana strain ITCC 4688 on the indigenous fungal diversity of an agricultural field was analysed. During the seven weeks of study B. bassiana became established within the field. In addition, a natural spread, as well as no effect on the diversity of the indigenous soil fungi was detected. As previously mentioned, in recent years additional different Otiorhynchus species have caused damage to numerous crops which are grown for horticultural purposes worldwide. The increasing extension of their geographic range is probably caused by climate change and/or an intensified international trade of infested plants. Several Otiorhynchus species are extremely polyphagous, have the potential to adapt to new host plants and reproduce by parthenogenesis. Those abilities may favour the establishment of an Otiorhynchus species in a newly colonised habitat. The genetic equipment of the weevils or the association with endosymbiotic bacteria may be responsible for the potential to adapt to new host plants or the parthenogenetic mode of reproduction. Therefore the endosymbiotical spectrum of four Otiorhynchus species was investigated. As one of the results, bacteria of the genera Rickettsia and ?Candidatus Nardonella? were detected. So far, the biological function of bacterial endosymbionts in Otiorhynchus spp. is speculative. However, new insights into the association of bacteria and weevils may be used in future to develop novel strategies for the control of Otiorhynchus pests.