In vitro assessment of the Larvicidal activity of Bacillus thuringiensis israelensis (Vectobac 12AS formulation) on Anopheles mosquito larvae

Abstract

This research aimed to evaluate the larvicidal activity of the lower doses of commercially synthetic Bacillus thuringiensis israelensis (Vectobac 12 Aqueous Solution (12AS)) 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 2022 using an aspirator and allowed to breed until the first instar larva appeared. The larvae were monitored and fed with 10% yeast until the third instar emerged. 240 healthy third instar larvae were selected and grouped into three treatments containing sixty (60) larvae each and replicated three times. The first, second and third treatments were respectively treated with 0.84, 0.42 and 0.21ml/l of Vectobac 12AS. Each treatment has a control containing twenty (20) larvae. Larval mortality was determined using a glass rod at an interval of 15 minutes for 24 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 1(6.7%) and 3(5.0%) were observed in the first treatment (0.84ml/l) after 15 and 30minute of exposure respectively. The highest mortality of 60(100%) was observed in all the treatments after 24 hours of exposure. Statistically, there was no significant difference (F=0.081, P> 0.05) . 2.35 ml/l, 5.54 ml/l and 8.15 ml/l was determined to be LC 50 , LC 90 and LC 99 respectively and LT 50 , LT 90 and LT 99 were found to be, 1809.29min and 2451.34min respectively. Conclusively vectobac 12AS has demonstrated a high level of efficacy as it revealed 100% 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 12AS.