Limited effects of glyphosate on the behaviour and immunity of males from six populations of the European earwig

Abstract

Abstract The use of herbicides on crops often results in unintentional, low-dose exposure of non-target organisms, such as insects. While these exposures are increasingly known to alter the survival and physiology of insects, it remains unclear whether these effects can vary between populations and modify other fitness-related traits, such as behaviour and immunity. Here, we addressed these questions by testing the effects of sublethal exposure to glyphosate (Roundup©) on the behaviour and immunity of European earwig males from six natural populations. We exposed each male to a dose of glyphosate that was either recommended for crops, five times lower than that recommended for crops, or to a control solution. Twenty-four hours later, we measured the activity, boldness, and aggregation of each male. We then exposed them to an entomopathogenic fungus, monitored their survival for 6 weeks, and measured the immune response of the survivors. We found a condition-dependent effect of glyphosate exposure on male activity. Exposure to low doses induced a positive association between activity and weight, which was not observed in the high-dose and control groups. Glyphosate had no effect on any of the other measured traits. All these results were consistent across the six populations tested, although we did find population-specific differences in almost all measurements on males. Further research is now needed to better comprehend the non-linear dose-response to glyphosate on male activity and to evaluate the effectiveness of detoxification processes in this species. Overall, these results emphasise the importance of investigating the effects of herbicides on insects to expand our general understanding of the use and potential risks of plant protection products in integrated pest management programs.