Effect of inactivation by sunlight on the larvicidal activities of mosquitocidal Bacillus thuringiensis H-14 isolates from Nigerian soils.

Bacillus thuringiensis H-14 is a well recognized bioinsecticide against mosquitoes. This study investigates the inactivation effect of sunlight on the larvicidal activities of four Nigerian isolates of B. thuringiensis H-14, code-named OBG1, OBG8, GSC3 and GNA13 as compared with a standard mosquito larvicide, B. thuringiensis var. israelensis (BTI). A 0.125 mg/1 suspension of spore-delta-endotoxin powder of each isolate was exposed to direct sunlight for 7 h on a concrete roof (ca. 13 m high). After exposure, the toxicity of each bacterial suspension to Aedes aegypti larvae was determined by bioassay. Three of the isolates, OBG8, OBG1 and GSC3 exhibited higher larvicidal activities than B.T.I. against A. aegypti larvae after exposure to sunlight. The resistance of Nigerian isolates to inactivation effects of sunlight advocates their potential in biocontrol of mosquitoes.