Bacillus thuringiensis israelensis VCRC B650 culture filtrate useful for mosquito oviposition attractant and larvicidal action

Oviposition attractants hold the potential attention for monitoring and controlling mosquitoes by enticing them to deposit eggs at specific locations. In this study, the bacterial culture filtrate of Bacillus thuringiensis var. israelensis VCRC B650, previously isolated from clay soil at an agricultural site in U.T of Puducherry, was investigated for the first time. This larvicidal bacterium was assessed for oviposition attractancy against dengue and filarial vectors, namely, gravid females of Aedes aegypti and Culex quinquefasciatus, respectively. The investigation revealed that, at 1:1 dilution of bacterial culture filtrate and water, Cx. quinquefasciatus exhibited significant attraction, with an oviposition activity index (OAI) value of +0.92, surpassing the standard threshold value of +0.30. The OAI of Bti culture filtrate at a 1:1 dilution was also compared with a standard oviposition attractant, p-cresol, at a concentration of 10ppm. It was observed that the Bti culture filtrate demonstrated a significant oviposition attractant effect, with 80 per cent more egg rafts laid, compared to p-cresol at 20 per cent. GC-MS analysis showed that there were 25 compounds present in the Bti culture supernatant, and out of those, only one compound, namely, benzaldehyde, was effective in showing oviposition attraction.