| The beet armyworm, Spodoptera exigua (Hiibner), is a worldwide distributed and polyphagous pest, which resistance is extensive and complex. In recent years, the damage caused by the beet armyworm increased dramatically in China. To clear the resistance level and biochemical mechanism of beet armyworm in Sichuan province, and make good use of insecticides and implement effective resistance management strategy, we surveyed the resistance of beet armyworm. Furthermore, effects of cyantraniliprole at sublethal concentrations on the development of Spodoptera exigua and the activities of three detoxifying enzymes were researched, which is the second entry from the anthranilic diamide class of insecticides. The results were summarized as follows:Diet-incorporation bioassays is adopted to establish the sensitive baseline of 9 classes of pesticides (chlorpyrifos, abamectin, emamectin benzoate, hexaflumuron, methoxyfenozide, indoxacarb, lambda-cyhalothri, chlorantraniliprole and cyantraniliprole) of beet armyworm. Spodoptera exigua collected from five regions from Sichuan were evaluated for their susceptibilities to the nine insecticides. The results show that, the resistance of beet armyworm from five field populations to lambda-cyhalothrin and abamectin were high universality. The resistance ratios of Spodoptera exigua from Ziyang to lambda-cyhalothrin and abamectin were 593.7 and 514.0-fold respectively with extremely high level resistance. And the resistance ratio of Spodoptera exigua from Shuangliu, Leshan and Suining to the two insecticides were ranging from 81.0 tol 36.5-fold, 8.9 to 50.0-fold respectively. Some populations including Shuangliu, Ziyang and Suining developed a low levels of resistance to chlorpyrifos, which resistance ratio were 5.1 to 7.6-fold. The field populations of Spodoptera exigua from Pengzhou, Shuangliu, Leshan and Suining developed a low levels of resistance even to a moderate levels of resistance to hexaflumuron, which resistance ratio were 5.3 to 16.2-fold. The beet armyworm populations from Pengzhou and Suining also show low to moderate resistance to methoxyfenozide, ranging from 5.2 to 21.1-fold. In addition to the Ziyang population to chlorantraniliprole was minor resistance with resistance ratio of 3.6-fold, all the populations were susceptible to a few novel insectieides, including indoxacarb, chlorantraniliprole, cyantraniliprole.The synergist assays suggested that CarE, GSTs and MFO might participate in the observed tolerance to lambda-cyhalothrin and abamectin in Spodoptera exigua, and also involve in the detoxification of Spodoptera exigua to other insecticides.When the larvae were treated with three sublethal doses of cyantraniliprole, their growth and reproduction were significantly restrained in the LC10, LC25 and LC50 groups compared to those in the control group, which of the inhibition rates of average weight were 11.55% to 50.36% and the developmental durations of the larvae from the 3rd instar larva to pupa in the LC25 and LC50 were elongated by 0.20 and 0.56 d, respectively. The pupation rates were 63.89%,49.43% and 30.17% and decreased clearly compared to the control (80.93%). The adult longevity was obviously shortened and the number of eggs laid per female and egg hatching rates decreased clearly compared to the control.The activities of carboxylesterase (CarE) and glutathione-S-Transferase (GSTs) in the Spodoptera exigua 3rd larvae treated with the sublethal doses of cyantraniliprole were promoted at the beginning and then decreased from 24 h to 96 h after treatment. The activities of mixed function oxidase (MFO) were also inhibited at 48 h and 72 h after treatmen. And the activities of MFO in the LC25 and LC50 groups were significantly lower than control, the higher the dose, the lower the enzyme activity. It shows that the inhibition be in proportion to the dosages. |
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