Evolutionary compromises to environmental toxins: ammonia and urea tolerance inDrosophila suzukiiandDrosophila melanogaster

Summary The invasive species Drosophila suzukii has evolved morphological and behavioral adaptations to lay eggs under the skin of fresh fruits. This results in severe damage of a wide range of small and stone fruits, thus making this species a serious agricultural and economical threat. Drosophila suzukii females typically lay few eggs per fruit, preferring not infested fruits. Hence larvae are exposed to a reduced amount of nitrogenous waste products. On the contrary, the innocuous Drosophila melanogaster lays eggs on fermented fruits already infested by conspecifics, with larvae developing in a crowded environment characterized by accumulation of nitrogenous waste such as ammonia and urea. Given these differences in oviposition and larval ecological niche, we expected different behavioral and physiological mechanisms in the two species to cope with nitrogenous waste. We investigated the impact of different concentrations of ammonia and urea on fecundity and larval development in both species. Females and larvae of D. suzukii showed a greater sensitivity to high concentration of both compounds, with a dramatic decrease in fecundity and egg viability. To better understand the pathways underlying these differences, we evaluated the effect on ornithine aminotransferase and glutathione-S-transferase, two enzymes involved in nitrogen metabolism and stress response that are expressed during larval development. Under ammonia and urea exposure, the expression of these enzymes was significantly reduced in D. suzukii . The fact that D. suzukii ’s shift from rotten to fresh fruit as oviposition and larval substrate resulted in less efficient detoxifying and excretory mechanisms represents a potential approach for its control. Fecundity and larval development are in fact dramatically impaired by nitrogen waste products. These findings can help in planning effective strategies of sustainable pest management that targets both females and larvae.