Eleven mosquitocidal Bacillus thuringiensis isolates from Nigerian soils were screened for the degree of toxicity against Aedes aegypti larvae. The six most larvicidal isolates, code-named OBGI, OBG8, BUS4, BAR3, GSC3 and GNA13, were identified as subsp. israelensis (B.t.i). Spores of the six isolates of a B. t. i. from a commercial powder (R-153–78, Roger Bellon Laboratory, Belgium) and of IPS 82 (Institut Pasteur (Standards)) were subjected to ultraviolet irradiation (280–350 nm) for up to 75 min. After irradiation, the toxicity of OBG8, OBGI, BUS4, and BAR3 was higher than that of R-153–78 but lower than that of IPS 82.
