Abstract
Mosquitoes are the carriers of severe well-known illnesses such as malaria, Japanese encephalitis, dengue fever, chikungunya fever, West Nile virus, yellow fever, lymphatic filariasis and zika virus. These diseases produce significant morbidity and mortalities in humans and livestock around the world. The present research investigated the toxicological and histological effects of three bacterial insecticide, Spinosad, Bacillus thuringiensis and B. sphaericus against the fourth-stage larvae of dengue and on zika virus vector, Aedes aegypti under laboratory as well as semi-field conditions. The lethal concentration to kill half (50%) of the population was found in Ae. aegypti fourth-instar larvae with LC50 0.005, 0.055, 0.414 ppm (laboratory conditions) and 0.007, 0.070, 0.563 ppm (semi-field conditions) respectively at 24 h.
In laboratory conditions, the tested effect of bacteria against larvae were 1.26, 1.27 and 1.35 folds compared with semi-field conditions. Also, these results indicate that mosquito larvae of Ae. aegypti were more susceptible to Spinosad than B. thuringiensi and B. sphaericus by about 9.59 and 77.12 folds respectively. The histological changes in mosquitoes targeted with bacterial insecticide were studied by light microscopy, evaluating the impact on mid-gut epithelial cells following treatment with LC50 of bacterial insecticide and the results showed detectable alteration in Gastric Epithelial Tissue (GEC) and fatty body (F). Overall, this study highlighted that bacterial insecticides can be proposed as effective tools for eco-friendly control of the dengue and Zika virus vectors.