Isolation of a Bacillus thuringiensis strain (serotype 8a:8b) highly and selectively toxic against mosquito larvae

An isolate of Bacillus thuringiensis designated as PG-14 obtained from the Philippines was highly toxic to the mosquitoes Aedes aegypti and Culex molestus but nontoxic to the silkworm, Bombyx mori, and adults of a daphnid. The degree of toxicity to mosquito larvae was the same as that of the reference strain of Bacillus thuringiensis subsp. israelensis (serotype 14). Parasporal inclusion produced by the isolate PG-14 was spherical or irregular in shape and morphologically similar to that produced by the reference strain of subsp. israelensis. The H antigenic structure of the isolate was identical to that of the reference strain of B. thuringiensis subsp. morrisoni (serotype 8a:8b). Differences were shown in the O antigenic structures and in the production of lecithinase. Thermostable exotoxin was not produced by the isolate PG-14. The results indicate the isolation of a B. thuringiensis strain which shows the same toxicity as that of subsp. israelensis.