TRAPP

Agriculture and vector control programs make intensive use of chemical insecticides to combat insect pests and disease vectors. While the main purpose of these insecticides is to kill insects considered harmful, some of them (e.g. DDT, organophosphates, neonicotinoids...) are criticized for their harmful effects on both biodiversity and human health. Insecticides represent a major selection pressure for insect populations, to which organisms can respond through mutation-selection processes, but also through phenotypic plasticity. Transgenerational plasticity (TGP) is a form of non-genetic inheritance in which a change in the phenotype of offspring is triggered by an environmental signal in the parental generation without involving genetic modification. There are many examples of TGP that are adaptive, but also maladaptive or even non-adaptive, particularly in the face of environmental stress. Nevertheless, by generating heritable phenotypic variations, TGP can influence the course of evolution. The existence of the TGP process is no longer disputed, but many questions remain, particularly as regards the immediate mechanisms that transmit these effects between generations, and the persistence of TGP over more than two generations. Worldwide pesticide consumption is estimated at two million tonnes a year, but the long-term consequences on ecosystems are manifold and far from understood. Over time, insecticides degrade, reducing the initial lethal deposit to a sublethal residue, triggering sublethal effects in animals that can be inherited transgenerationally. Predicting the intensity of these sublethal effects is complicated in the context of global warming by the strong influence of temperature. In this project, we propose to use the experimental power offered by Drosophila melanogaster, a model species in physiology, developmental biology and genetics, to explore TGP in response to insecticides. We will use a protocol that allows us to disentangle the genetic and non-genetic contribution to the heritability of phenotypic variance. Molecular mechanisms linked to TGP, particularly epigenetics, will be studied. This species can also be considered as a sentinel species, representative of insect species exposed to contaminants in most agroecosystems, such as the Drosophila sp. community and the related pest species D. suzukii, but observations can probably be generalized to other arthropods. The study of the transgenerational impacts of insecticides is still little taken into account in insecticide risk assessment. Our project will therefore provide original experimental data on 1) the extent of TGP in response to sublethal insecticidal effects over a wide range of insecticide modes of action and phenotypes, 2) the genetic variability (between genotypes within and between populations) of TGP as well as its sensitivity to climate change, 3) the persistence of the transgenerational phenotypic response over generations and 4) the underlying molecular mechanisms.