Comparative susceptibility of wild and laboratory-reared Aedes and Anopheles larvae to ivermectin.

Background: Administering ivermectin to humans and livestock renders their blood toxic for mosquitoes like Anopheles and Aedes, offering a promising approach for controlling these vectors. However, the impact of such treatment on larval stages exposed to the drug through contaminated breeding sites is not fully understood. This study looked at how ivermectin affects the development of Aedes and Anopheles larvae.

Methods: Four instars laboratory-reared (Anopheles gambiae Kisumu strain and Aedes aegypti Bora Bora strain) and wild-derived (Anopheles coluzzii VK5 and Ae. aegypti Bobo) larvae were exposed to ivermectin-medium containing the molecule at concentrations ranging from 0 to 100 ng/ml for 24 h, then transferred surviving larvae into ivermectin-free medium to monitor development until adult stage and female fecundity. Parameters measured were: larval survival, pupation dynamics, teneral emergence rates, and fecundity of the adult females in terms of numbers of eggs developed and laid. Two independent experiments were performed, each with four biological replicates. Data obtained for each life history parameter were compared between treatments to characterize ivermectin effects.

Results: Data indicated that highest ivermectin concentrations (100, 75, and 50 ng/ml) reduced larval survival by over 50% within 24 to 48 h post-exposure, with varying effects across different strains. Wild-derived larvae showed lower susceptibility to ivermectin compared to laboratory larvae for both Anopheles and Aedes species. The concentrations leading to 50% larval mortality (4-day-LC50) were 3.65 and 1.86 ng/ml for Anopheles VK5 and Kisumu strains, and 15.60 and 2.56 ng/ml for Aedes Bobo and Bora Bora strains, respectively. Notably, while high concentrations severely impacted larval development, low concentration (1 ng/ml) appear to be a sublethal concentration and allowed for adult emergence. No significant effects on the number of laid eggs were observed across the different strains.

Conclusion: Overall, these data showed how development parameters of laboratory-raised and wild-derived Anopheles and Aedes larvae are affected differently by ivermectin, highlighting potential implications for vector control strategies and ecological concerns regarding non-target organisms and environment persistence. Further investigations are planned to understand existing mechanisms allowing wild-derived larvae to better survive than laboratory ones despite the presence of ivermectin in their breeding environment.