Mosquito adulticidal activity of a biosurfactant produced by Bacillus subtilis subsp. subtilis.

Background: A biosurfactant, surfactin, produced by a strain of Bacillus subtilis subsp. subtilis (VCRC B471), was effective in killing mosquito larval and pupal stages. As it was lethal to the non-feeding pupal stage, it was presumed that it could kill the adult mosquitoes also. In this study, the adulticidal effect of the biosurfactant was assessed in the laboratory against a malaria vector, Anopheles stephensi.

Results: The biosurfactant surfactin, separated from the culture supernatant of the production strain, showed mosquito adulticidal activity when tested as ultralow-volume (ULV) spray in a Peet-Grady chamber. Knockdown activity and mortality were found to increase with increasing surfactin dosage. Knockdown dosage (KD) and lethal dosage (LD) were calculated by statistical analysis. The KD(50) and KD(90) dosages were 10.73 and 26.39 mg m(-3) respectively. The LD(50) and LD(90) dosages were 16.13 and 39.21 mg m(-3) . The average droplet size of B. subtilis surfactin was 17.5 ± 1.07 µm.

Conclusion: The present study indicates that the biosurfactant surfactin, produced by B. subtilis subsp. subtilis (VCRC B471), is a potential bioadulticide for ULV spray against malaria-transmitting Anopheles stephensi mosquitoes. This is the first report of a mosquito adulticide from a microbial source.