Efficacy of Bacillus thuringiensis var israelinsis (Bti) on Culex and Anopheline mosquito larvae in Zomba

Abstract

Laboratory based experiments were conducted using Bacillus thuringiensis var israelinsis (Bti) to establish the efficacy of Bti on Anopheles and Culex mosquito larvae from Zomba. The study evaluated two formulations of Bti namely VectoBac® WG and VectobaBac® 12AS against selected species of mosquito larvae. During this study, six different concentrations of Bti were set and 360 mosquito larvae were exposed to these different concentrations and results were observed hourly for 10 hours, then 24 hours and 48 hours. The experiment was replicated three times. Results show that the lower effective dosage that can be used to control Culex mosquito larvae in Zomba after 48hours of exposure is 47.73g/ha. The LT50 and LT90 being 7.5hrs and 24.3 hrs respectively. On the other hand, Anopheles mosquito larvae require 103.41g/ha of Bti which is almost double as much as that required by Culex. Anopheles LT50 is 6.2 hrs and LT90 is 18.5 hrs. In addition, it was observed that when Culex and Anopheles mosquito larvae were exposed to the same dosage of liquid formulation of Bti (0.001ml/L) there was no significant difference in their mortalities. Following the successful results of Bti in controlling mosquito larvae at laboratory level it is our recommendation to ask the Government of Malawi to come up with a policy to allow the use of Bti in controlling mosquito larvae in Malawi