Mosquito pupicidal toxin production by Bacillus subtilis subsp. subtilis

A strain of Bacillus subtilis exhibiting mosquito larvicidal and pupicidal activity was identified as B. subtilis subsp. subtilis by partial gyrA sequence. A study of the association of growth and sporulation in the production of the mosquitocidal toxin and the susceptibility status of different mosquito species is presented here. The pupal stages of Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti [LC50 (μg/ml) 2, 7.3 and 11.8, respectively] were found to be more susceptible to the Crude Mosquitocidal Toxin (CMT) than larval stages [LC50 (μg/ml) 19, 23 and 34, respectively] with An. stephensi being the most susceptible species. The LT50 of freshly molted pupae of An. stephensi, when exposed to an LC90 (6.82 μg/ml) dosage of CMT, was found to be 1.17 h. Maximum biomass production was achieved at 48 h (15.46 g/l) and maximum production of the CMT was observed at 24 h (1.12 g/l) of growth. Mosquitocidal toxin production was found to be associated with vegetative growth of the organism rather than with sporulation since the mosquitocidal activity was initiated after the lag phase and the maximum mosquitocidal activity was obtained at 12 h, much earlier than the initiation of sporulation. The mosquitocidal toxins of B. subtilis may be a prospective alternative in mosquito control programs involving bacterial biopesticides.