Effectiveness of a new granular formulation of biolarvicide Bacillus thuringiensis Var. israelensis against larvae of malaria vectors in India

Abstract

Control of vector(s) or mosquitoes, in general, through biolarvicide as an alternate biocontrol agent is a greatest desire. We evaluated a water-dispersible granular formulation biolarvicide Bacillus thuringiensis var. israelensis (Bti, H-14 serotype; VectoBac(®) WDG) in the laboratory and also in the field against two principal malaria vectors, Anopheles culicifacies and Anopheles stephensi. Laboratory evaluations against laboratory-reared immature of the two species were carried out at a temperature of 28°C ± 2°C and 70%-80% relative humidity. Field trials were conducted in a rural area and in Bangalore city, Karnataka, South India. First trial against the rural vector An. culicifacies was carried out in stone quarry pits at dosages of 0.05, 0.2, and 1 g/m(2). The second trial against urban vector An. stephensi was carried out in ring wells at 0.05, 0.1, 0.2, 0.5, and 1 g/m(2) dosages. Laboratory tests revealed increased efficacy against An. stephensi. The fifty percent lethal concentration (LC(50)) and LC(90) values against An. culicifacies and An. stephensi were 0.348 and 1.008 mg/L (χ(2) = 8.49; p > 0.05) and 0.245 and 0.533 mg/L (χ(2) = 4.67; p < 0.05), respectively. Based on the findings of no pupal production in the field, the formulation was effective up to 14 days at 0.2 g/m(2) or more appropriately at 0.25 g/m(2) dose for both the species under field conditions. We discuss how this new formulation was evaluated against An. culicifacies and An. stephensi under laboratory and field conditions. No adverse effects were observed on the nontarget species such as frogs, their tadpoles, small local fish, Notonectid bugs, and water scatters. We conclude that VectoBac WDG is effective at 0.25 g/m(2) and be recommended for its use in the vector-borne disease control program under integrated vector management concept.