Abamectin exposure causes chronic toxicity and trypsin/chymotrypsin damages in Chironomus kiiensis Tokunaga (Diptera: Chironomidae).

Abamectin has been extensively used in paddy fields to control insect pests. However, little information is available regarding its effects on non-target insects. In this study, we performed acute (3rd instar larvae) and chronic toxicity (newly hatched larvae <24 h) to determine the toxicity effects of abamectin on Chironomus kiiensis. The median lethal concentration (LC) values of 24 h and 10 d were 0.57 mg/L and 68.12 μg/L, respectively. The chronic exposure significantly prolonged the larvae growth duration and inhibited pupation and emergence. The transcriptome and biochemical parameters were measured using 3rd instar larvae exposed to acute LC and LC for 24 h. Transcriptome data indicated that five trypsin and four chymotrypsin genes were downregulated, and RT-qPCR verified a significant expression decrease in trypsin3 and chymotrypsin1 genes. Meanwhile, abamectin could significantly inhibit the activities of the serine proteases trypsin and chymotrypsin. RNA interference showed that silencing trypsin3 and chymotrypsin1 genes led to higher mortality of C. kiiensis to abamectin. In conclusion, these findings indicated that trypsin and chymotrypsin are involved in the abamectin toxicity against C. kiiensis, which provides new insights into the mechanism of abamectin-induced ecotoxicity to chironomids.