Transgenerational Consequences of Imidacloprid Larval Diet Contamination in the Sheep Blowfly Lucilia sericata (Diptera: Calliphoridae)

Pesticides have been extensively used in agriculture, forestry, and veterinary medicine under intensive production systems. Unfortunately, pesticide pollution resulted in a significant decline in non-target organisms, for instance, in detritivores such as necrophagous insects. Even formulations proposed as less harmful alternatives, such as neonicotinoids like imidacloprid (IMI), have been demonstrated to permeate the trophic chain and trigger severe consequences on non-target species. Here, the intra- and inter-generational effects of a sublethal dose of IMI were explored in the necrophagous greenbottle fly, <i>Lucilia sericata</i> (Meigen, 1826) (Diptera: Calliphoridae). This is because it has been demonstrated that the carcasses of domestic and wild animals can be contaminated with levels of these neonicotinoids. Transgenerational effects, extending up to three generations after a focal application of the pesticide on laboratory-cultivated F₁ flies, were investigated in this study. Morphological, demographic, and phenological features were evaluated through various analyses, including general linear mixed models (GLMM) and Haldane units analyses. Although GLMM showed no significant differences between treatments for the multiple traits observed, a significant directional microevolutionary trend of increased average imago and pupal size was identified for the IMI treatment through Haldane unit analysis. This microevolutionary change falls within the threshold of transgenerational phenotypic plasticity, a crucial mechanism for adaptive responses to environmental stressors. Among the possible explanations for this pattern, it is proposed that this is a likely consequence of the triggering of an epigenetic hormetic transgenerational change. This may contribute to explaining the development of adaptation and resistance towards pesticide formulations in a few generations after focal exposure. In addition to this idea, other possible mechanisms and consequences that explain the observed pattern are discussed. Overall, this experiment highlights the concerns of pesticide spillover consequences, even from sublethal doses of these formulations.