Characterization and mosquitocidal potency of a Bacillus thuringiensis strain of rice field soil of Burdwan, West Bengal, India

Bacillus thuringiensis is the most popular mosquitocidal bacteria, strains of which are effective against almost all mosquito larvae. It has host specificity and thus, has no adverse effect on non-target species of the ecosystem. Culex tritaeniorhynchus, a vector of Japanese encephalitis (JE), breeds in vast area of rice fields in Burdwan district of West Bengal, India, which has already confronted JE epidemic. Entomological investigation and ecological studies on this vector mosquito showed that JE epidemic may reoccur anytime in the area. A strain of Bt (BU55) was isolated from rice field soil, efficacy was tested against Cx. tritaeniorhynchus and mosquitocidal role was confirmed against Cx. quinquefascistus also. The LC50 of Bacillus thuringiensis BU55 against Cx. tritaeniorhynchus and Cx. quinquefascistus after 72 h was 8.59 ml (final dose 2.49 x107 CFU/ml) and 7.52 ml (final dose 2.20 x 107 CFU/ml), respectively. Insecticidal crystal protein profile of BU55 produced 136.89, 64.80, 43.45, 33.65 and 26.98 kDa bands. Among them 136.89, 64.29, 26.98 kDa proteins are comparable to actual toxins viz. Cry1Ac (138.3 kDa, Lepidoptera specific), Cry4D (68.0 kDa, Diptera specific) and Cyt (27.4 kDa, Diptera specific). The results clearly showed that the Bt strain is a potent dipteran larvicide and can be used against the JE vectors to control the disease. •The strain was isolated from rice field soils and it was effective against Culex tritaeniorhynchus which breeds in rice field water. Thus application of the microbe which is a part of the ecosystem will not impose any adverse effect on the ecosystem.•The strain was effective against Cx. tritaeniorhynchus as well as Culex quinquefasciatus.•The Cry proteins (Cry1Ac −136.89, Cry4D −64.80) and Cyt protein (Cyt – 26.98) would work synergistically to suppress the mosquito larvae.•The diptera specific (Cry4D −64.80 and Cyt – 26.98) and lepidoptera specific (Cry1Ac −136.89) proteins can also act against other dipterans and lepidopterans.•Presence of amylase, protease, lipase make this strain active against plant pathogens too.