Variation in the Activity of Three Principal Detoxifying Enzymes in Major Sucking Pest of Tea, Helopeltis theivora Waterhouse (Heteroptera: Miridae) from Sub-Himalayan Tea Plantations of West Bengal, India

摘要

Helopeltis theivora Waterhouse (Heteroptera: Miridae), is a major sucking pest of tea in North East India along with other tea growing countries. In West Bengal, tea is cultivated in three sub-Himalayan regions, Terai (foothill plains western to river Teesta), the Dooars (foothill plains eastern to river Teesta) and the Darjeeling hill slopes. Most plantations, in these regions are managed conventionally i.e. by spraying different synthetic insecticides and a few by organic farming using different herbal and microbial insecticides. In conventional plantations, continuous application of insecticides may lead to the selection of more tolerant H. theivora populations making the pest difficult to control. So, there is a pressing need to know the biochemical variability in relation to the metabolic resistance in the pest populations and develop a population specific control strategy. Activity of three principal insecticide detoxifying enzymes in H. theivora populations were studied from three tea growing regions of North Bengal. Higher levels of activity of all the studied enzymes were found from conventional tea plantations. In male H. theivora, the activity of general esterases (GEs) was 6.6-11.2 and 10.5-11.4 fold higher, cytochrome P450 (CYPs) was 2.0-3.2 and 3.0-3.2 fold higher and glutathione S-transferase (GSTs) was 5.2-8.3 and 6.4-8.7 fold higher in Terai and the Dooars populations, respectively than organic populations from Darjeeling hill slopes. Similarly, in female H. theivora, activity of GEs was 6.2-10.3 and 8.3-9.6 folds higher, CYPs was 1.9-3.2 and 3.0-3.3 fold, and GSTs was 3.5-5.4 and 4.4-6.0 fold higher in Terai and the Dooars, respectively than the organic populations from Darjeeling hill slopes. The activities of all three enzymes were found to be significantly low in organic plantations from Darjeeling hill slopes. Esterase I-VI isozymes with higher level of expression were found in specimens from conventional tea plantations than organic populations of H. theivora from Darjeeling hill slopes in isozymes study.