Genetic and molecular studies of olfaction in Drosophila

Partial compensation of the sublethal effect of deltamethrin on the sex pheromonal communication of Trichogramma brassicae

Pyrethroid insecticides are widely used and lead to a sizable environmental pollution that could interfere with the population biology of insects. Trichogramma is a beneficial insect used in biological control and which natural populations contribute to the control of Lepidopterus pests. In this work, we determined the effect of a sublethal dose of deltamethrin on the sex pheromonal communication of Trichogramma. The dose used (LD 0.1) induces no detectable mortality (the theoretical mortality is only one insect over 1000) and can be a good representation of contamination by this insecticide from environmental pollution. The insecticide was shown to have opposite effects on the sex pheromonal communication of Trichogramma, depending on which sex was exposed (Delpuech, J.M., Legallet, B., Terrier, O., Fouillet, P., 1999. Chemosphere 38, 729-739). We show that, when both sexes are simultaneously exposed to the insecticide, this effect is only partially neutralized. The mean response of treated males responding to the sex pheromone from treated females is not significantly different from that of controls, but the kinetics of their response is not the same. When both sexes are treated, the response of males to the sex pheromone is lower at the beginning but their response does not decrease during time contrary to controls and becomes finally higher than that of controls. Therefore, the sublethal effect of deltamethrin in the field can be either advantageous or disadvantageous depending on the difficulty in finding females and their scarcity.

Smell and taste perception in Drosophila melanogaster larva: toxin expression studies in chemosensory neurons

GAL4-driven targeted expression of tetanus toxin light chain (UAS-TeTxLC) in a subset of chemosensory neurons of the larval antennomaxillary complex (AMC) and pharynx causes abnormal chemosensory behavior in Drosophila melanogaster. Consistent with strongest staining in the dorsal organ (DO), the presumed olfactory organ of the AMC, tetanus toxin-expressing larvae subjected to an olfactory preference assay show anosmic behavior to most volatile substances tested. Furthermore, we observed reduced responses to sodium chloride, fructose, and sucrose in gustatory plate assays. Surprisingly, the entire subset of labeled sensory neurons from the terminal (maxillary) organ (TO) of the AMC was found to project via the antennal nerve to the larval antennal lobe region. The maxillary nerve remained completely unstained. Hence, a subset of neurons from the TO builds an anatomical entity with projections from the DO. Our results suggest that the AMC contains both olfactory and gustatory sensilla, and that the DO is the main olfactory organ in larvae.