Context and exposure history shape insecticide sensitivity in Drosophila melanogaster

Insecticide toxicology often overlooks how lethal and sublethal exposure impacts organismal performance in different contexts. This study examined Drosophila melanogaster's response to three insecticides with varying modes of action - acetamiprid, chlorantraniliprole, and deltamethrin - across multiple factors such as developmental stages, sexes, adult ages, and ambient temperatures.

The results revealed significant variation in insecticide sensitivity depending on these conditions, with temperature modulating toxicity differently for each compound. Deltamethrin proved highly lethal even at concentrations over 10,000 times lower than recommended field application rates.

Surprisingly, brief pre-exposure to any of the insecticides reduced lethality upon subsequent exposure to the same compound, with noticeable tolerance developing within 24 hours. Moreover, environments that improved tolerance to insecticides also decreased resilience to other environmental stresses like heat or nutrient starvation, indicating a potential trade-off in stress resilience.

Interestingly, acetamiprid exposure affected reproductive performance in a dose-dependent manner, reducing egg production but increasing developmental success in offspring. Despite this, the total number of surviving offspring remained unchanged.

In conclusion, this research underscores that insecticide susceptibility is highly dependent on biological context, environmental conditions, and recent exposure history. It introduces the concept of compound-specific, short-term, potentially costly tolerance as an unexplored consequence of insecticide exposure. The study emphasizes the need to consider these factors in pesticide risk assessment.