Resistance Monitoring Of Spodoptera Litura And The Resistance Mechanisms To Indoxacarb

The common cutworm, Spodotera litura (Fabricius), is a world-wide distributed agricultural pest. Indoxacarb was a novel pesticide belonging to the oxadiazine class with unique action mechanism. Indoxacarb is one of the few insecticides that could control S. litura very well.In recent years, the field common cutworm in Malaysia has developed very high resistance to indoxacarb. Thereofore.the study on indoxacarb resistance is very important for sustainable control of the S. litura. In this paper, the monitoring of the field resistance, resistance selection and resistance mechanisms were carried out. The major objectives were to evaluate the risk of the S. litura developing resistance to indoxacarb and to understand the resistance mechanisms underlying it.(1)The studies were carried out to evaluate resistance in the populations of S. litura from five districts of Hunan Province to10insecticides from2010to2013using a standard leaf dip bioassay method. For organophosphates, carbamates and pyrethroids, resistance ratios compared with a susceptible strain were in the range of13.5-229-fold for organophosphates,37.5-1069-fold for carbamates and12.3-227-fold for pyrethroids. The resistance ratios were in the range of1.45-42.6-fold that lower than conventional insecticides.(2)Based on the bioassay results, indoxacarb was used to select susceptible strain of S. litura under40%-70%selection pressure. After8continuous generations of selection with indoxacarb, the selection population obtained15.63folds of resistance compared with its unselected population. By calculating the realized heritability of resistant population was0.325. When the mortality was80%-90%, resistance of S. litura to indoxacarb reached100folds only need7to9generation. The results showed that S. litura have high risk of developing resistance to indoxacarb in a short period.(3)Activity of carboxylesterase, glutathioneS-transferase and multifunction oxidase of susceptible strain and selected strain of S. litura were tested. The results showed that activity of carboxylesterase in selected strain was2.22times than the unselected strain. But the activity of glutathione S-transferase and multi-function oxidase in selected strain were1.00and1.02times than the unselected strain with no siginificant difference. We can infer that resistance of S. litura to indoxacarb had relation with carboxylesterase.