Enhancement of Resistance vis-à-vis Defence-Enzyme Activity in Tea Mosquito Bug, Helopeltis theivora Waterhouse (Hemiptera: Miridae) Selected Through Exposure to Sub-lethal Dose of Monochrotophos

Abstract

Tea industry is the back bone of agro-economy of the tea producing regions. Tea mosquito bug, Helopeltis theivora Waterhouse is one of the most devastating sucking pests of tea and is a menace to tea plantations of North Bengal and other states of NE India. Insecticide forms the mainstay of pest management programme in tea plantations. Insecticide stress and selection have led to the development of high tolerance or resistance in many pests including the sucking bug H. theivora. LC50 value of an organophosphate insecticide, monochrotophos (SL 36 %) to this species increased about 105 fold when selected by exposure to sub-lethal dose for three generations. Generation-wise relative tolerance level when selected by sub-lethal dose of monochrotophos showed a significant increase in 1st and 2nd filial generations as compared to the parental generation (P < F1 < F2). General esterases (GE) activity got enhanced by 5.32 and 16.4 fold, and the activity of cytochrome P450 monooxygenases (CYP) increased by 1.96 and 9.50 fold in F1 and F2 generations respectively as compared to parental generation. The generation-wise increase in relative resistance and the activity of defence enzymes were found to have high positive correlation; r = 0.999 for GE and r = 0.994 for CYP. The study suggests that the titres of GE and CYP in H. theivora can be used as the markers of relative tolerance to insecticides in general, with mode of action similar to monochrotophos. Such defence-enzyme based detection technique for tolerance levels may help early identification of resistant population of H. theivora; hence its management.