Neurotoxic pesticide thiacloprid impairs Drosophila fecundity by disrupting germline stem cell differentiation and somatic cell apoptosis in ovary.

Thiacloprid (THI), a cyano-substitued neonicotinoid, is widely used in agriculture and has been identified as a critical factor responsible for the global decline of non-target insects due to its persistent environmental residues. Here, we investigated the developmental and reproductive toxicity of THI in Drosophila melanogaster using sublethal concentrations (0.5, 5, 10 mg/L) referenced to previously reported sublethal THI levels in laboratory. The results showed that THI exposure significantly reduced larval body length by 22.6 % and pupation rate by 30.4 %. LC-MS analysis revealed a pronounced sex-specific accumulation of THI residues between adult ovaries (1.997 pg/ovary and 15.997 pg/ovary) and testes (0 pg/testis and 1.229 pg/testis). Chronic THI exposure disrupted oviposition, ovarian morphology and GSC/CB homeostasis in both ex vivo and in vivo conditions. Mechanistically, we found that THI could induce premature germline stem cell (GSC) differentiation through dpp downregulation and subsequent bam upregulation in GSC progeny, and triggered apoptosis in escort cells. Similarly, THI exposure impaired testes GSC differentiation and induced somatic cell apoptosis, resulting in a marked reduction in sperm counts by 40 %. Collectively, these findings highlight the ecological risk posed by THI residues to the reproductive fitness of non-target insects in nature.