Insecticide resistance among field populations of Hyposidra talaca Walker (Geometridae: Lepidoptera) in tea plantations of Assam, India: detection through a biochemical approach

The black inch looper, Hyposidra talaca is a serious defoliator pest of tea and its management relies profoundly on application of insecticides. Here, we investigated the insecticide susceptibility in H. talaca collected from six districts of Assam to five insecticides: bifenthrin and deltamethrin (Pyrethroids), quinalphos (Organophosphates), emamectin benzoate (Avermectins) and flubendiamide (Diamides). Based on relative susceptibility values, all populations showed varied levels of susceptibility to the insecticides evaluated as compared to the susceptible population. Tinsukia and Dibrugarh populations showed high LC(50)s to most of the insecticides assessed. A moderate to high level of resistance was recorded for deltamethrin [Resistance coefficient (RC) = 19.03-31.75; Resistance ratio (RR) = 8.23-38.90]. Bifenthrin showed moderate level of resistance [RC = 11.80-23.79; RR = 16.52-25.52] while quinalphos demonstrated low-resistance level [RC = 4.35-6.06; RR = 3.22-4.41]. Emamectin benzoate and flubendiamide were effective against H. talaca in all tested populations, except for Tinsukia and Dibrugarh populations where low levels of resistance were recorded. Detoxification enzyme assays indicate that glutathione S-transferases (GST), general esterase (GE) and cytochrome P450 (CYP) activities were high in all field populations as compared to susceptible ones. GE and CYP had significant variation among different population and registered positive correlation with the LC(50)s of deltamethrin, bifenthrin and quinalphos. Synergistic assays reveal that the use of synergists' piperonyl butoxide, S.S.S.-Tributylphosphorotrithioate and ethacrynic acid in combination with deltamethrin and quinalphos re-establishes the toxicity of these insecticides. The findings show that detoxification enzymes play important role in the development of resistance to insecticides in H. talaca and will be useful in designing resistance management programmes against the pest.