Biological evaluation of chitosan from the black soldier fly (Hermetia illucens) against Culex pipiens

The increasing resistance of mosquitoes to conventional insecticides and the environmental impacts associated with their use have stimulated interest in sustainable alternatives. Although chitosan has attracted attention as a biologically active and biodegradable biopolymer, the larvicidal efficacy of chitosan derived from the black soldier fly, Hermetia illucens , against Culex pipiens and its associated biochemical effects remain insufficiently characterized. This study aimed to evaluate the efficacy of an H. illucens -derived chitosan preparation against different mosquito developmental stages and investigate the biochemical responses associated with exposure. Chitosan was extracted from H. illucens larval exuviae through demineralization, deproteinization, and alkaline deacetylation. Its larvicidal activity was evaluated against different developmental stages of C. pipiens at concentrations of 25, 50, 100, and 200 µg/mL after 24 and 48 h of exposure. Lethal concentrations (LC₅₀, LC₉₀, and LC₉₅) were estimated using probit analysis. Larval and pupal survival were assessed after exposure of third-instar larvae to the 48-h LC₅₀, and changes in neuromuscular and digestive enzyme activities, antioxidant defenses, and oxidative stress biomarkers were measured in surviving larvae 24 h after exposure. The extracted chitosan preparation produced concentration- and time-dependent mortality across mosquito developmental stages. First-instar larvae were the most susceptible, whereas pupae were the least susceptible. For third-instar larvae, the LC₅₀ values were 26.09 µg/mL at 24 h and 25.53 µg/mL at 48 h. At the 48-h LC₅₀ exposure, larval and pupal survival declined to 53.0% and 45.33%, respectively. Exposure was associated with reduced acetylcholinesterase (AChE), gamma-aminobutyric acid transaminase (GABA-T), superoxide dismutase (SOD), glutathione-S-transferase (GST), catalase (CAT), and reduced glutathione (GSH), whereas α- and β-esterase activities increased. Amylase and lipase showed only marginal reductions (0.8% and 1.0%) of uncertain biological relevance. Lipid peroxidation and total protein carbonyl content also increased, indicating enhanced oxidative stress. This study characterizes both the larvicidal activity of H. illucens -derived chitosan and the associated biochemical responses in C. pipiens . The findings indicate that the extracted preparation affects mosquito survival, enzyme activities, antioxidant defenses, and oxidative stress biomarkers. Further research is needed to establish the underlying mechanisms, characterize the preparation more fully, and evaluate its environmental safety and potential for mosquito management.