Exposure to a glyphosate-based herbicide does not alter maternal care and offspring quality in the European earwig

Sublethal exposure to pesticides can affect the reproduction and population dynamics of many non-target organisms, such as insects. Among these pesticides, glyphosate-based herbicides (GBHs) were long thought to have no effect on insects because their active compounds can only affect plants and microorganisms. However, a growing body of evidence suggests that GBH can directly or indirectly alter a wide range of fitness-related traits in insects. In this study, we tested whether exposure to the GBH Roundup© affects maternal care behaviour and juvenile development, locomotion and immunity in the European earwig, an insect commonly found in vineyards and orchards. First, we exposed female earwigs to Roundup at concentrations ten times below, equal to and ten times above the normal application rate (NAR) and then measured the expression of maternal care in terms of egg collection, egg and juvenile care and defense. We also measured maternal self-grooming and locomotor activity, and the development time, weight and size of newly produced juveniles. In a second experiment, we exposed earwig juveniles to a control solution or to Roundup and then measured their locomotion, the expression of genes involved in their development (the juveniles hormone pathway), and their survival after exposure to a fungal pathogen. Overall, our results showed no significant effect of Roundup on any of the parameters measured. This finding suggests that direct exposure to a GBH formulation may not necessarily induce behavioural, physiological and developmental alteration in this species. It also calls for future studies to explore the underlying mechanisms behind this apparent lack of sensitivity. More generally, these results highlight the importance of assessing the impact of pesticide use and the factors driving potential resilience across a wide range of non-target organisms to ensure sustainable agricultural practices.