Effects of plant extracts on the behaviour and physiology of the Odontotermes obesus (Ramb.) (Isoptera: Termitidae)

Abstract

Plant chemicals are an important group and naturally occurring crop protectants that are usually safer to humans and the environment than conventional pesticides with minimal residual effect. The effects of leaf and seed extracts from five plants (Dodonaea viscosa, Adhatoda vasica, Jatropha curcas, Moringa oleifer ,and Ocimum basilicum) on Odontotermes obesus (Ramb.) were evaluated in laboratory. The crude leaf and seed extracts of these plants prepared with different non-polar to polar solvent viz., petroleum ether, n- hexane, chloroform, methanol, ethanol, acetone and water. These extracts were used for bioassay in soil to determine the mortality, change in tunneling behavior, and gut enzymes of workers along with soldiers of the termites. The n-hexane leaf extract of D. viscosa in the soil showed lower LT50 (104.41, 95.53 and 66.68 hours at 1, 5 and 10% concentrations, respectively) than the other plants extracts. The tunneling activities of O.obesus in D. viscosa n-hexane extract suppressed in soil treated with 1, 5 and 10% concentration with minimum tunnel length (63.00, 36.33, 16.67 respectively) than other plants extracts. The active chemical agent of the most effective plant Dodonaea viscosa leaf extract was isolated through gel filtration was used at 1, 5 and 10% concentrations in the final bioassay for determination of lethal time (LT50) for mortality and also activities of total esterase, protease and cellulase enzymes in the mid gut of workers of O. obesus. A reduction in activities of gut protease’s and cellulase’s in the termites collected from plant extract treated soil was observed.