Two and a Bud 59:55-59, 2012 RESEARCH PAPER Comparative susceptibility and detoxifying enzyme activities to fenpropathrin in field-collected and laboratory-reared Oligonychus cofJeae infesting tea A. Roobakkumar', A. Babub, V.K. Jasin Rahman', M. Sankara Rama Subramaniam' and D. Vasantha Kumar' 'Division of Entomology, UPASI Tea Research Institute, Nirar Dam B.p.a., VaJparai 642 127, Coimbatore District, Tamil Nadu, India b Department of Entomology, Tea Research Association, Tocklai Experimental Station, Jorhat - 785 008, Assam, India ABSTRACT Variability in fenpropathrin toxicity to eight populations ofthe red spider mite, Oligonycllus coffeae, was determined by leaf disc bioassay method. The different populations used in the experiment were collected from different tea growing regions of south India, viz. Valparai, Coonoor, Gudalur(famil Nadu), Vandiperiyar, Munnar, Mepadi (Kerala) and Koppa (Karnataka) and a laboratory susceptible population. Mite populations from Vandiperiyar region exhibited higher resistance (RR = 2.13) when compared to the susceptible population. General esterase activity with a- napthyl acetate as substrate was more in the field collected populations than in the susceptible laboratory population. Increased glutathione-S- transferase (GST) activity was detected in the field-collected populations by using l-chloro-2, 4- dinitrobenzene as substrate and the resistance ratio varied between 1.11 and 1.86. Esterase separation by native polyacrylamide gel electrophoresis (P,'\G E) showed significant relationship between resistance ratio and band patterns. These results suggest that continuous monitoring of fenpropathrin susceptibility, determination of resistance patterns and implementation of resistance management strategies are warranted. INTRODUCTION Mites deserve special attention in view of their widespread occurrence as pests in all the tea growing regions of southern India. Among them, the red spider mite (RSM), Oligonychus cofJeae (Nietner) (Acarina: Tetranychidae), is an important pest causing considerable crop loss in tea. Severe infestation by this mite ultimately leads to defoliation. In south India, control of 0. cofJeae is mainly achieved by synthetic acaricides. The high reproductive potential and short duration of lifecycle, combined with frequent application of synthetic acaricides, facilitate rapid development of pesticide resistance in spider mites. A very high level of resistance to several compounds can develop within one to four years of continuous use and can often induce a high degree of cross-resistance (Cranham and Helle, 1985). Fenpropathrin (a-cyano-3-phenoxybenyl 2, 2, 3, 3- tetramethyl cyclopropane carboxylate) is a synthetic pyrethroid with repellent and contact activities, which is used as a selective insecticide/acaricide (Thomson, 1995). 55 It has been effectively applied against many species of spider mites belonging to Tetranychus, Eotetranychus and Panonychus (Muraleedharan and Ambalatharasu, 1983). Fenpropathrin was recommended for the control of 0. cofJeae and the compound has been used extensively during the last one decade (Selvasundaram and Muraleedharan, 2003). Recently, the practitioners have experienced a decline in the efficiency of fenpropathrin even at high rate of application. Periodic monitoring is an integral part of the effective management of resistance in 0. cofJeae infesting tea. Therefore, the present study was undertaken to detect resistance in field populations of 0. cofJeae, if any, to fenpropathrin and to conduct biochemical assays to evaluate differences in esterase activity. MATERUUSANDMETHODS The acaricide tested was a commercial formulation of fenpropathrin (Meothrin 30 EC; Sumitomo Chemical India Pvt. Ltd., Hyderabad). All other chemicals used in the