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 collected within Zomba district. The study evaluated two formulations of Bti namely VectoBac® WG and VectobaBac® 12AS against selected species of mosquito larvae. Mosquito samples were collected using two methods; Adult blood-fed female mosquitoes and larvae from their breeding sites. Adult mosquitoes laid eggs and hatched into larvae. While those collected from the field as larvae were allowed to emerge into adults and got blood-fed with Rattus norvegicus Albinus, then laid eggs and hatched into larvae. Third in star larvae were used in all experiments. 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 after 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 48 hours of exposure is 47.73g/ha of Bti, the LT50 and LT90 being 7.5 hrs and 24.3 hrs, respectively. On the other hand, Anopheles mosquito larvae required 103.41g/ha of Bti which is more than double as much as that required by Culex. The LT50 and LT90 for Anopheles were 6.2 hrs and 18.5 hrs respectively. 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. Both liquid and granular Bti have shown to be effective against mosquito larvae, hence this has a direct impact in reducing populations of adult mosquitoes and consequently a reduction in the transmission of Malaria, Lymphatic filariasis and other diseases that are spread by mosquito bites.