PLANTDETER · Plants olfactory deterrent signals

Final Activity Report Summary - PLANTDETER (Plants olfactory deterrent signals)

Our project was to test if plants protected by molecules that are toxic to insects are also emitting repellent chemicals to warn insects off. The hypothesis exposed in this project was that plants which are producing an insecticide might use odorant molecules to repel insects before so that they are not exposed to the insecticide. On an evolutionary scale, this mechanism would delay the selection of resistant insects. As a case test, we used plants producing phytoecdysteroids. Phytoecdysteroids are molecules produced by plants that mimic the insects' moulting hormone. Insects specifically need this hormone to shed their old cuticule and to form a new one. These molecules are steroids which are not toxic to mammals. Several plants consumed by humans contain such molecules, like spinach and quinoa. We selected a group of plants known to produce phytoecdysteroids, e.g. Chenopodiaceae from which spinach is a good example. Many Chenopodiaceae produce phytoecdysteroids while others don't. According to our working hypothesis, phytoecdysteroid-positive plants should produce repellent odorant molecules. As a test insect, we used European corn borer larvae which are known to attack many plants in the world. From our previous work, we knew that larvae from this insect detect phytoecdysteroids as bitter molecules because they are equipped with specific taste receptors for them. Using a locomotion compensator borrowed from the company SYNTECH, we tested if larvae that were just borne would spontaneously orient towards odours from maize and go away from odours emitted by plants producing phytoecdysteroids. We demonstrated that European corn borer larvae are strongly repelled by odors from spinach while they are attracted to odours from maize plants. However, the attraction towards maize was stronger if the odour was pulsed and a continuous odor of maize was found to be repellent. We also found that phytoecdysteroids-positive plants are repellent to European corn borer larvae while some phytoecdysteroids-negative plants were attractive. However, a few of Chenopodiaceae which are phytoecdysteroid-negative were also repellent, some of them emitting very oily or fish-like odours. These observations support our initial proposition that well defended plants emit odours to repel insects and suggest that odours might be used by plants as aposematic signalling for their ennemies.

Data: CORDIS, © European Union