The tea mosquito bug, Helopeltis theivora Waterhouse, from the Dooars tea plantations, North Bengal, India, was tested for susceptibility change and resistance development to endosulfan. Six different H. theivora populations collected from six subdistricts of the Dooars and their responses to endosulfan were investigated by probit analysis and compared with those of a susceptible reference strain. Resistance ratio and resistant coefficient for endosulfan ranged from 582.18 - 1504.20 folds and 5.78 - 14.95, respectively (based on LC95). Selection of adults of H. theivora in laboratory to various sub-lethal concentrations of endosulfan up to five generations resulted in maximum mortality at highest concentration in every successive generation. The resistance ratio for the fifth generation increased 4.417 fold as compared to first generation. The results indicate that endosulfan should be avoided for managing endosulfan resistance inH. theivora.
Key words: Helopeltis theivora, Dooars tea plantations, susceptibility change, endosulfan, resistance.
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