Geographical variation in susceptibility of tea red spider mite, Oligonychus coffeae (Nietner) (Acari: Tetranychidae) to commonly used acaricides in tea plantations of Assam, north east India

Abstract

ABSTRACTThe tea red spider mite, Oligonychus coffeae, is one of the most destructive pests of tea in the world which is mainly managed by chemical acaricides. In the present study, concentration-mortality responses of O. coffeae from eight tea geographical populations along with a laboratory susceptible strain against five acaricides, viz., ethion, dicofol, propargite, fenazaquin and fenpropathrin were assayed based on standard leaf-dipped method. Although observed levels of susceptibility varied between populations and acaricides, population from Cachar region registered a high LC50 value to most of the acaricides evaluated. Almost all of the tested field populations had developed high to very high level of resistance to ethion and dicofol, with resistance ratios ranging from 13.58 to 134.27-fold. Fenazaquin and propargite were very effective against O. coffeae in all tested populations, while fenpropathrin showed minor variation in their susceptibility. Significant positive correlation was only observed between the LC50 values of ethion and dicofol (r = 0.95, P = 0.005) suggesting the potential for cross-resistance. These results indicated that control failure was associated with resistance to ethion and dicofol therefore reinforcing the need of resistance management program and offered useful information about alternative acaricides to control O. coffeae.