Aphicidal Efficacy of Chitinase-Producing Bacteria Isolated from White-Grub Gut against Mustard Aphid, Lipaphis erysimi (Kaltenbach)

Abstract

The present study was conducted to evaluate the insecticidal potential of chitinase-producing bacterial isolates obtained from the gut of white grub against mustard aphid, Lipaphis erysimi (Kaltenbach), under laboratory conditions. Two promising chitinolytic bacterial isolates, HS3, identified as Stenotrophomonas sp., and LL5, identified as Sphingobacterium multivorum, were selected for bioassay. The insecticidal efficacy of live bacterial cultures, heat-killed cultures and culture supernatants was evaluated at three concentrations, viz., 10⁻⁵, 10⁻⁶ and 10⁻⁷, using the leaf-dip method. The experiment was conducted in a completely randomised design with seven treatments and three replications, and mortality was recorded at 24, 48 and 72 hours after treatment (HAT). Aphid mortality varied with bacterial isolates, treatment preparation, concentration and exposure period, and generally increased with increasing exposure period. Among the treatments, the live culture of Stenotrophomonas sp. HS3 recorded the highest mortality of 80.00 per cent at a 10⁻⁷ concentration at 72 HAT, followed by Sphingobacterium multivorum LL5 with 73.34 per cent mortality. Culture supernatants also exhibited considerable insecticidal activity, whereas heat-killed cultures recorded comparatively lower mortality. The results demonstrated the insecticidal potential of gut-associated chitinase-producing bacteria, particularly Stenotrophomonas sp. HS3, against L. erysimi. Further studies involving purified chitinase, characterisation of extracellular metabolites and evaluation under greenhouse and field conditions are required to establish their potential as biological control agents.