Susceptibility of Musca domestica L. to soil-occurring Bacillus thuringiensis (Berliner) isolates

The oral toxicity of various soil occurring isolates of Bacillus thuringiensis (Berliner) collected in Sardinia (Italy) and Angola (Africa) was evaluated by laboratory bioassays against the housefly Musca domestica L. B. thuringiensis isolates were characterized by morphological (presence of parasporal inclusions), genetic (16S rRNA gene sequence, detection of cry genes) and protein pattern analysis (SDS-PAGE). Houseflies employed in the bioassays were reared in our laboratory in order to use standardized larvae and adults. Bioassays were performed by incorporating the spore-crystal mixtures into an artificial diet. Insects were exposed to appropriate diets which provided adequate nutrition for the whole duration of the test. Spore-crystal mixture of the bacterial isolates exhibited different toxicity levels. The highest toxicity on adults was exhibited by Sardinian isolates, while isolates from Angola did not show significant toxicity against housefly adults or larvae. Since the toxicity reached against M. domestica was only weak or moderate, further investigations are needed to detect an appropriate strain of B. thuringiensis in the perspective of an efficient microbiological control of the housefly.