Insecticidial effect and mixtures screening of tenvermectin B for controlling Plutella xylostella (L.)

Tenvermectin B is a patented novel macrocyclic lactone insecticide independently developed in China. In order to develop its potential market and delay the emergence of resistance, the insecticidal activities of tenvermectin B to 10 pest varieties, such as Plutella xylostella, Pyrausta nubilalis, and Hyphantria cunea, were performed by leaf dipping method. The activities against Aphis gossypii, Tetranychus urticae, and Liriomyza sativae were conducted by spraying method. Sun Yunpei's co-toxicity (CTC) method was used to evaluate the synergistic effect of the mixtures of tenvermectin with thioacetamide, chlorfenapyr, and indoxacarb on P. xylostella, and the optimal ratio was employed for field efficacy assay. The bioassay showed that tenvermectin B had higher control activity against P. xylostella, P. nubilalis and T. urticae, compared with abamectin, the LC₅₀ values were 0.115, 0.043, and 0.012 mg/L, respectively. Tenvermectin B also displayed high activity against Mythimna separata, H. cunea, Cnaphalocrocis medinalis, Frankliniella occidentalis and A. gossypii, the LC₅₀ values ranged from 0.337-9.784 mg/L. Mixture screening showed that tenvermectin B with neither thiotraniliprole nor indoxacarb had synergistic effect on P. xylostella. The mixture of tenvermectin B and chlorfenapyr showed significant synergy against P. xylostella, with a CTC value of 178.59 at the optimal ratio of tenvermectin B to chlorfenapyr as 1 : 14 (m : m). The result of the field trial indicated that at 7 d and 14 d after treatment, the control efficacies of the mixture against P. xylostella were over 80% at the dosage of 75 g a.i./hm². Our study demonstrated that tenvermectin B had a broad insecticidal spectrum, with excellent activity against P. xylostella, T. urticae, A. gossypii, etc., showing promising potential for development and application. The mixture of tenvermectin B and chlorfenapyr (1 : 14) showed a synergistic effect and could be further developed for P. xylostella control to delay the emergence of resistance.