Comparative sensitivity to UV-B radiation of two Bacillus thuringiensis subspecies and other Bacillus sp.

Susceptibility of Bacillus thuringiensis spores and toxins to the UV-B rang e (280-330 nm) of the solar spectrum reaching Earth's surface may be respon sible for its inactivation and low persistence in nature. Spores of the mos quito larvicidal B, thuringiensis subsp. israelensis were significantly mor e resistant to UV-B than spores of the lepidopteran-active subsp. kurstaki. Spores of subsp. israelensis were as resistant to UV-B as spores of B. sub tilis and more resistant than spores of the closely related B. cereus and a nother mosquito larvicidal species B, sphaericus. Sensitivity of B. thuring iensis subsp, israelensis spores to UV-B radiation depended upon their cult ure age; 24-h cultures, approaching maximal larvicidal activity, were still sensitive. Maximal resistance to UV-B was achieved only at 48 h.