Toxicological effects and defense mechanisms induced by beta-cypermethrin in Drosophila melanogaster

Widespread use of the pyrethroid insecticide beta-cypermethrin (beta-CYP) has led to adverse effects on nontarget populations within agroecosystems. Despite the efficacy of beta-CYP in pest control, its toxicological and defense mechanisms remain incompletely understood. In the present study, we explored the toxicological effects, antioxidant mechanisms and immune response against beta-CYP using Drosophila melanogaster, a well-established model organism for the study of insect biology, to represent the broader class of nontarget organisms. We exposed Drosophila larvae to 0.667 μg/mL beta-CYP and revealed that delayed development and caused intestinal epithelial damage in larvae. To gain insights into the molecular underpinnings of these effects, RNA sequencing analysis and quantitative polymerase chain reaction validation were performed. These analyses revealed that the messenger RNA levels of glutathione S-transferase were increased, third instar larvae exhibited an increase in reactive oxygen species content and a corresponding increase in antioxidant enzyme activity in response to beta-CYP exposure, indicating an upregulated response to oxidative stress. Beta-CYP also activated Hippo pathway to resist apoptosis and promote cell proliferation. Moreover, beta-CYP induced melanization and Toll immune pathways involved in immune response in Drosophila larvae, specifically the Toll pathway gene Drs. This activation suggests that Drosophila increases antioxidant defenses and promotes mitosis in damaged tissues as compensatory mechanisms to mitigate the cytotoxic effects of beta-CYP. These findings provide new insight into the mechanisms of beta-CYP-induced toxicity and the defense mechanisms in insects; they may also inform strategies for the sustainable use of insecticides and the development of mitigation measures to protect nontarget species in agroecosystems.