In vitro assessment of the Larvicidal activity of Bacillus thuringiensis israelensis (Vectobac ۱۲AS formulation) on Anopheles mosquito larvae

This research aimed to evaluate the larvicidal activity of the lower doses of commercially synthetic Bacillus thuringiensis israelensis (Vectobac ۱۲ Aqueous Solution (۱۲AS)) against the fourth instar larva. One hundred and fifty blood-fed female anopheles mosquitoes were collected from different resting sites from Abuja Quarters in June ۲۰۲۲ using an aspirator and allowed to breed until the first instar larva appeared. The larvae were monitored and fed with ۱۰% yeast until the third instar emerged. ۲۴۰ healthy third instar larvae were selected and grouped into three treatments containing sixty (۶۰) larvae each and replicated three times. The first, second and third treatments were respectively treated with ۰.۸۴, ۰.۴۲ and ۰.۲۱ml/l of Vectobac ۱۲AS. Each treatment has a control containing twenty (۲۰) larvae. Larval mortality was determined using a glass rod at an interval of ۱۵ minutes for ۲۴ hours. ANOVA was used to statistically analysed differences in the larval mortality between the treatment and probit analysis was used to determine the lethal concentration (LC) and the lethal time (LT). Mortality of ۱(۶.۷%) and ۳(۵.۰%) were observed in the first treatment (۰.۸۴ml/l) after ۱۵ and ۳۰minute of exposure respectively. The highest mortality of ۶۰(۱۰۰%) was observed in all the treatments after ۲۴ hours of exposure. Statistically, there was no significant difference (F=۰.۰۸۱, P> ۰.۰۵). ۲.۳۵ ml/l, ۵.۵۴ ml/l and ۸.۱۵ ml/l was determined to be LC۵۰, LC۹۰ and LC۹۹ respectively and LT۵۰, LT۹۰ and LT۹۹ were found to be, ۱۸۰۹.۲۹min and ۲۴۵۱.۳۴min respectively. Conclusively vectobac ۱۲AS has demonstrated a high level of efficacy as it revealed ۱۰۰% larval mortality even at a lower recommended dose. Further research should be carried out to study the impact of other biological and environmental factors on the efficacy of vectobac ۱۲AS.

Keywords:

Aedes aegypti , Bacillus sphaericus , Bio-larvicide , biological control , Dipterans , Malaria Control Strategy