Prior Exposure to DEET Interrupts Positive and Negative Responses to Olfactory Cues in Drosophila Melanogaster

While the high efficiency of N,N-diethyl-meta-toluamide (DEET) in protecting humans against disease-transmitting arthropods is unquestioned, the mode of action of DEET on a physiological and behavioural level remains debated. Recent advances demonstrated that DEET modulates the function of the insects' odorant receptor complex. In this study we aimed to evaluate how DEET affects the behaviour of insects towards attractive and repellent odours. In a series of experiments with larvae and adults of the fruitfly Drosophila melanogaster, we were able to provide the first evidence that DEET, applied in a gaseous phase, interrupts not only positive but also negative responses to olfactory cues indicating that insects treated with DEET lose the ability to perceive and respond to odours. This effect was also observed if insects were exposed to DEET prior to but not during the behavioural experiments, but was reversible after some time. DEET functioned as deterrent in experiments where insects had direct contact to the substance. This dual function - the camouflage of hosts from a distance and the deterrence upon contact - may be the key for the high efficiency of DEET.