Plants have designed a range of sustainable strategies to defend themselves against insect predation. The best-known are insecticide molecules like nicotine, pyrethrinoids or moulting hormone analogs. That plants still use such defences is a wonder, considering how fast insect pests adapt to insecticides. We presume plants are using a range of strategies to keep using such defences over a long time. One of these strategies could be to send conspicuous olfactory signals to deter insects from approaching or landing on them.
We propose to search for and quot; warning and quot; molecules in a range of plants well defended against insects. Warning signals would serve to deter insects before intoxicating them and thus lessen the chances of selecting resistant insects. Our target plant group will be plants producing phytoecdysteroids, which represent a distinct class of plant secondary compounds that are analogues of insect moulting hormones. We propose to collect and analyse odours released from plants producing phytoecdysteroids, look at common patterns between them, evaluate if they are emitted in larger quantities when plants are subjected to a stress and when the metabolism of their defences is activated, and evaluate their biological activity on polyphagous ins ect pests.
The rationale supporting this research is that herbivore insects assess the quality of their food before ingesting it, or before laying eggs on a host plants. Demonstrating the existence of such warning signals would be of great interest for agriculture since they could be used to prolong the efficiency of existing natural or artificial defences, or integrated in pest management strategies aimed at diminishing the impact of pest insects rather than destroying them. Given the expected limitations of the use of pesticides and the general will of consumers to be provided pesticide-free food, we need to design new crop protection strategies against insects feeding on plants that are sustainable and environment-friendly.
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