Screening of Highly Toxic Bacillus thuringiensis and its Effects on the Growth and Development of Spodoptera exigua (Lepidoptera: Noctuidae)
Yang, Xiaolin; Oluwafemi, Akinkurolere Rotimi; Zhang, Hongyu
In this study, the toxicity of Bacillus thuringiensis YL-17 to Spodoptera exigua (Hübner 1808) was screened from 23 stock B thuringiensis isolates. Its lethal and sublethal effects on the development and mortality of S exigua were evaluated, and the LC50 values were determined. The LC50s of pure crystals, pure spores and the spore-crystal complex were 22.1μg/ml, 230.2μg/ml and 20.2μg/ml, respectively. The toxicity of B thuringiensis YL-17, stemmed mainly from its crystal. B thuringiensis YL-17 did not affect the hatch rate of eggs, but the neonate mortality increased signifcantly (P<0.05) with an increase of treatment concentration and egg age. The spore-crystal complex signifcantly (P<0.05) inhibited the growth of the third instar larvae, signifcantly (P<0.05) extended the larval development, and caused a signifcant (P<0.05) reduction in the weight of pupae, the pupation rates and the adult emergence rates of larvae that survived. However, there was no signifcant effect of the spore-crystal complex (P=0.18) on adult sex ratio of larvae that survived. These results suggest that besides killing S exigua larvae, B thuringiensis YL-17 also influences the development of larvae and pupae of this pest.