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Insect Molecular Biology

Major Research Themes

• Parasitoid Host interactions
• Innate Immunity
• Tolerance Mechanisms

Research Programmes

• The existence of asexually reproducing parasitic wasps is an evolutionary riddle. Solitary parasitoid wasps developing inside another insect, usually the immature stages of another insect species, are locked into an ongoing evolutionary adaptation process. While wasps evolve to overcome the defence system of the host insect, host populations in turn adapt to the threat of an intruding parasitoid. This is a classical ‘Red Queen’ paradigm, where the contestants continuously evolve to stay in the parasitoid-host relationship. Given the extreme selection pressures of the relationship, where one of the two organisms will invariably perish, it is apparent that the two insects rely on sexual recombination of existing genetic diversity to evolve. Nevertheless, a number of parasitoid species are known to reproduce asexually. The implication is that an asexual mode of reproduction engenders some benefit, which constitutes a driving force to overcome, at least temporarily, the adaptive requirement to recombine genetic material. We are testing genotype fixation as a possible drive for asexual reproduction.
  

  Contact Researcher: Otto Schmidt, Harry Roberts

• Invertebrates are able to overcome injury and invading microorganisms using several innate reactions involving proteolytic cascades leading to localized blood clotting and to melanization, the latter process involving production of cytotoxic molecules, the phagocytosis of bacteria and apoptotic cells, the encapsulation of larger parasites by blood cells, and the induced synthesis by the fat body of a battery of potent antimicrobial peptides, which are secreted into the hemolymph, where they act synergistically to kill the invading microorganisms. The insect host defence system shares many of the basic characteristics of the mammalian acute phase response, especially at the level of the coordinate control of gene expression, where similar cis-regulatory and inducible trans-activators appear to play key functions. However, despite the powerful techniques developed to study the genetics of Drosophila, our understanding of the innate immune response is still largely unknown. We want to know how the extracellular molecular environment is perceived by cells and organisms and how the corresponding signals are translated into cellular actions. We are using parasitoid-mediated immune evasion and suppression as a model system for targeting molecular recognition and defence genes.

  Contact Researcher: Otto Schmidt

• Most arthropod species fight intruding parasites and pathogens by coagulation and encapsulation reactions, which are adapted to the unique properties of an open circulatory system. In addition, immune activity is observed outside the hemocoel, such as the epidermis and the gut lumen, where cell-free defence reactions form a first line of defence against potential intruders. We have studied the induction of the prophenoloxidase-activating cascade in lepidopteran by feeding larvae sublethal doses of Bt-toxin formulations, which revealed an elevated immune response involving increased melanization and coagulation. Likewise, a Bt-resistant strain from the field showed elevated immune reactions, including the presence of soluble toxin-binding lipid particles in the hemolymph and gut lumen. The elevated immune-status and Bt-tolerance can be transmitted to the next generation, whereby reciprocal genetic crosses showed that only females transmit Bt-tolerance to offspring. We are investigating the new tolerance mechanism against pathogens and toxins based on a systemic immune-induction that can be transmitted from one generation to the next by a maternal effect.

  Contact Researcher: Otto Schmidt