Semiochemicals and olfactory protein in mosquito control

This thesis reports a biochemical study on the olfactory system in mosquitoes, which pose one of the major threats to human health, in order to devise strategies alternative to insecticides for population control. In particular, the final aim of the research work was the discovery of new mosquito repellents. Our approach has been developed along two parallel lines: a) a biochemical research on the proteins mediating odour perception in mosquitoes, in particular a functional study of Odorant-binding proteins (OBPs) and Chemosensory proteins (CSPs), two classes of polypeptides involved in the detection and recognition of olfactory stimuli in insects. b) a structural comparison of the main components of essential oils behaviourally active on mosquitoes, in order to extract common feature that might provide guidelines for the design of better repellents; The experimental work has been focused on the expression of OBPs and CSPs in mosquitoes. Using a proteomic approach, applied to antennae and pre-adult stages (in particular eggs, larvae and pupae) we have identified OBPs and CSPs that are more likely involved in odour recognition. These proteins were expressed in bacterial system and used in ligand-binding assays with compounds bioactive on mosquitoes. During the last decade, we have witnessed an increasing number of publications dealing with mosquito repellents, most identified in plant essential oils. This large amount of research was stimulated by recent concerns on the safety of DEET, the commercial repellent. We have concluded that the best strategy for designing more efficient repellents is to aim at compounds with lower volatility, that provides a longer permanence on the skin as well as a reduced odour intensity. Based on this idea and taking the structures of some known repellents as templates, we have designed new molecules by introducing additional polar groups in the molecule and/or increasing their molecular weight. The new chemicals have been tested in “warm body” and “human-bait” experiments and several of them proved to be as good to repel mosquitoes as those currently used