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DETECTION OF INSECTICIDE RESISTANCE IN DIAMONDBACK MOTH (PLUTELLA XYLOSTELLA , LINNAEUS : PLUTELLIDAE)

MANUJUM, KITIYAPORN., SOMBOON, SUNGWARL., PIMSAMARN, SUPANEE.

Insecticide Toxicology and Environmental Laboratory, Entomology Department,
Faculty of Agriculture, Khon Kaen University, Thailand


      The diamondback moth, Plutella xylostella  Linnaeus (Plutellidae : Lepidoptera) is a serious pest of cruciferous crops where various classes of insecticides were used intensively. Field strains of the diamondback moth collected from seven cruciferous vegetable plantations from four provinces ; Khon Kaen, Nakhon Ratchasima, Petchaboon and Udon Thani ; were examined for levels of insecticide resistance to abamectin, Bacillus thuringiensis  subspecies aizawi  (Bta), Bacillus thuringiensis  subspecies kurstaki  (Btk), chlorfenapyr and profenofos when compared with a susceptible strain. Insecticide bioassays were carried out by leaf dip feeding method using third instar, generation 2 and generation 10, larvae. Median lethal concentrations (LC50) were determined by probit analysis from which resistance ratios were calculated. Resistance to abamectin, Bta, Btk and profenofos were observed with the resistance ratios of 2- to 84- fold, 1- to 15- fold, 1- to 15- fold and 1- to 9- fold, respectively. No resistance to chlorfenapyr was found from all collected field strains.

      Enzyme activities were assayed by a spectrophotometric method using microplate reader. Activities of general esterase, glutathione S-transferase and oxygenase were significantly higher (P < 0.05) in resistance strains compared with those in a susceptible strain. No significant different (P > 0.05) was found in activity of aetylcholinesterase.

      The levels of detoxification enzyme activity, general esterase and oxygenase, were correlate with varying levels of resistance in different strains suggesting that both enzymes may play an important role in diamondback moth resistance. Moreover, biochemical microassays proved to be an alternating method for monitoring insecticide resistance in field populations of the diamondback moth.

ที่มา : การประชุมวิชาการสมาคมพิษวิทยาแห่งประเทศไทย ประจำปี 2548 Food & Chemical Safety วันที่ 17-18 พฤศจิกายน 2548 โรงแรมแกรนด์ ทาวเวอร์อินน์ ถนนพระรามหก กรุงเทพฯ