Pheromone perception in an insecticide-contaminated environment : info-disruption or adaptation? – PHEROTOX

Using behavioural, electrophysiological, cellular and molecular approaches, we investigated the effects of sublethal doses of insecticides after adult treatments on the response of adult males to the sex pheromone throughout the olfactory pathway. We studied these effects on the behavioural response and its plasticity in a wind tunnel or an arena bioassay. At the physiological level, we studied effects on electrophysiological responses of olfactory neurons in the antennae and within the antennal lobes. At the molecular level, we analysed effects on the transcriptome and/or the proteome of the brain and antenna to investigate regulatory mechanisms. We focused more particularly on gene families involved in olfactory plasticity (genes coding for hormones, biogenic amines and their respective receptors), detoxification, and genes encoding targets of the insecticide clothianidin: the nicotinic receptors.

We found an unexpected positive effect of a low dose of an insecticide on the oriented behaviour and central olfactory neuron sensitivity to the sex pheromone in male moths. This effect is re-inforced in experienced (pre-exposed to the pheromone) moths. These results, as well as the characterization of nicotinic acetylcholine receptors, have been discussed with professionals and international specialists at a symposium organised by the PI and the international cluster Vegepolys.

Through this project we want to evaluate unexpected potential risks of insecticide residues on the populations of their target insects. A better understanding of the mechanisms of action of these molecules on the olfactory system should allow to develop new pest management strategies at long term, by taking into account the possible risks/advantages induced by the presence of pollutants at low doses on the efficiency of insecticide treatments.

The results of the project have been published in 4 scientific papers in international peer-reviewed journals. They have been presented at 4 international conferences, 3 national conferences at several european Universities and research institutions and at the symposium « Pherotox », organised by the PI and the international cluster Végépolys at Angers in January 2016.

Most animals live in an “odour world” and depend strongly on chemical stimuli to get information on their biotic and abiotic environment. In insects such as Lepidoptera, which include many important agricultural pests at the larval stage, males are attracted by sex pheromones emitted by conspecific females. Although integrated pest management strategies are increasingly developed, most insect pest treatments rely on neurotoxic chemicals, including neonicotinoid insecticides. These molecules such as the widely used, last generation insecticide clothianidin are known to disrupt synaptic transmission through nicotinic acetylcholine receptors. The wide-spread use of neurotoxic insecticides results in residual accumulation of low concentrations in the environment. This environmental stress probably acts as an “info-disruptor” by modifying the chemical communication system, and therefore decreases chances of reproduction in target insects. However, low doses of pollutants can induce a non-expected hormesis effect by enhancing reproduction abilities. Low insecticide doses might thus induce adaptive processes in the olfactory pathway of target insects, which could allow them to bypass this stress, favouring the development of insecticide resistance. Although the effect of sublethal doses of insecticides have been shown to alter various behaviours of beneficial insects such as honeybees, little is known on the adaptive mechanisms to the stress caused by insecticides developed in lepidopteran pests. Previous data show that sublethal doses of insecticides disrupt the behavioural response to sex pheromone in many insect species, but the mechanisms underlying this disruption have not been clarified. Here we aim at investigating the adaptive mechanisms of the olfactory system of noctuid moths as a response to the stress caused by sublethal doses of neonicotinoid insecticides from the behavioural to the cellular level. In noctuid moths we have previously shown different forms of neuronal olfactory plasticity, which show that responses to pheromone can be modulated as a function of physiological state or previous experience, rendering the moth an excellent model for our project.
Using behavioural, electrophysiological, and molecular approaches, we will investigate the effects of sublethal doses of clothianidin after larval (which is the target stage of most field treatments) and adult treatments on the response of adult males to the sex pheromone throughout the olfactory pathway. We will test effects on the behavioural response to sex pheromone and its plasticity in a wind tunnel. At the physiological level, we will study effects on electrophysiological responses of olfactory neurons on the antennae and in the antennal lobes. Effects on the moth brain will also be investigated using calcium imaging and brain volumetry techniques. At the molecular level, we will analyse effects on both the transcriptomes and proteomes of the antennae and the brain, in order to highlight regulated processes. Specific attention will be given to gene families 1) known to be involved in olfaction such as genes coding for olfactory receptors and detoxification enzymes, and 2) known as targets for clothianidin: the nicotinic receptors.
This project takes advantage of the complementary expertise, which has been acquired by our two teams in Angers (molecular and cellular effects of insecticides on nicotinic receptors/plasticity of insect olfaction) and Versailles/Paris (physiological, cellular and molecular aspects of peripheral olfactory events). Our results will give new insights in the mechanisms of sensory adaptation of pest insects to a polluted environment. These data will be important for the future development of new strategies in insect pest management, by taking into account the possible risk/benefit induced by the increasing presence of pollutants at low doses on the efficiency of treatments.