STUDIES ON ACETYLCHOLINESTERASE AND ITS POSSIBLE ROLE IN INSECTICIDE RESISTANCE OF MAJOR PEST OF TEA, Helopeltis theivora FROM DARJEELING FOOTHILLS PLANTATION

Tea, Camellia sinensis (L.) O. Kuntze is a perennial and monoculture crop growing over extensive areas of Darjeeling hills, Terai and the Dooars regions. It provides an inexhaustible resource for colonization of the tea mosquito bug, Helopeltis theivora Waterhouse that cause substantial damage to the tea crop. Insecticides like organophosphates and pyrethroids are regularly applied to control this pest. Acetylcholinesterase (AChE) act by binding to the neurotransmitter (acetylcholine) in some synapses of the nervous system in many pests. The objective of this study was to investigate the quantitative and qualitative differences in the acetylcholinesterase in cerebral ganglion of this sucking bug, and then to compare between specimens that maintained in laboratory conditions and those collected from pesticide exposed tea plantations. A significantly high level of activity of the acetylcholinesterase was evident in the cerebral ganglia homogenate of the pesticide-exposed individual. Comparison of isozyme profiles also showed a common basic pattern with only one acetylcholinesterase band with Rm value of 0.13 that was observed both in pesticide exposed as well as laboratory maintained individual. The field-collected specimens showed deeply stained band indicating an intensive formation of AChE, which tells us much about the insecticide resistance level of this sucking pest. AChE based detection technique would be helpful for easy detection of the pesticide resistance status of this tea pest in near future.