Studies On Mechanism And Management Of Pesticides Resistance Of Plutella Xylostella

Diamondback moth (Plutella xylostella L.), which belongs to Lepidoptera Plutellidae, is an important worldwide pest to cruciferous vegetables. It causes-serious damage to cruciferous vegetables such as cabbagQ(Brassica oleracea var. Capitata), cauliflower(5. oleracea var. Botrytis) and greengrocery. So vegetable production is seriously tlireatened. To provide theoretical basis for Plutella xylostella integrated control,studies on the dynamics of resistance development to phoxim, the dynamics of AchE and CarE, the relationship between temperature and pesticides toxicity, the relationship between pesticides toxicity and different diamondback moth development stages,were conducted. The results are summarized as follows:1. The rapid resistance development could be seen in the resistance selection result of phoxim to diamondback moth. The LC50 of phoxim to F0 generation was 297.014mg/L but that of phoxim to F12 generation was 1343.747mg/L,which was 4.524-fold as that of F0. Significant difference existed between the LC50 of phoxim to F0 and F12. It indicates resistant population has come into being.2. The studies on the resistance mechanism of diamondback moth showed that the AchE activity increased quickly during the selection process, which rose from 0.5312nM-mg'PrlSmin-1 (F0) to 3.1467uM-mg-1Pr l5min-1 (F12), and increased by 5.924-fold. The great difference could been seen. Difference in the activity of CarE also existed between F0 and F12. The activity of CarE rose rapidly, that of F12 was12.768-fold as that of F0.3. The toxicity tests results of 2 pesticides on different diamondback moth development stages were as follows, the LC50 values of 5% fipronil SC(suspension concentration) to 1-4 instars larvae were 0.640 mg/L, 0.683 rng/L, 1.009mg/L and 1.210mg/L respectively and those of Avermectins EC(emulsifiable concentration) to 1-4 instars larvae were 1.185mg/L, 1.610mg/L, 1.717mg/L and 2.342mg/L respectively. The LC50 of both insecticides to the larvae of diamondback moth increased with the increase of instars. In other words, the sensitivity of different instars larvae to the two insecticides decreased with the development stages. Moreover, the LC50 value of Avermectins increased faster than that of fipronil4. The toxicity test result of insecticides to 3rd instar larvae under different temperatures showed that the lethal effect of fipronil, Avermectins and phoxim enhanced with temperatures increase. This suggested that the 3 insecticides were all positive-temperature pesticides.At 17℃,2rC,25℃,29℃ and 33℃, the LC50 value of cypermethrin to 3rd instar larvae of Plutella xylostella were 363.069mg/L, 217.409mg/L, 264.673mg/L, 186.237mg/L and 176.904mg/L respectively. The LC50 values of cypermethrin increased with the increase of temperature between 21 ℃ and 25℃. This showed could explain cypermethrin was a negative-temperature pesticide within this temperature range. Otherwise, cypermethrin was positive-temperature pesticide within 17 ℃ ~21 ℃ and 25℃ ~33℃.5. Cotoxicity test of Avermectins and fipronil mixtures showed that synergism existed at the five chosen ratios.The cotoxicity coefficients were 238.84,177.32,455.90,246.93 and 221.48 respectively.