Effect of bacillus thuringiensis cab109 on the growth, development, and generation mortality of spodoptera exigua (Hübner) (lepidoptera: Noctuidea)

Abstract

The efficiency of Bacillus thuringiensis (Bt) CAB109 on Spodoptera exigua (Hübner) (Lepidoptera: Noctuidea) larvae was investigated. This study introduces a novel concept of generation mortality (GM) was introduced. Bt CAB109 suspensions at sub-lethal concentrations of 0, 102, 103, 104, 105, and 106 cfu/ml were prepared and used to treat the second instar larvae of S. exigua. The results showed that the mortality rates of the larvae were 5.0, 8.3, 15.0, 23.3, 36.7, and 55.0% respectively after 7 days of treatment. The mean weights of treated larvae with different concentrations were 2.63, 2.19, 2.03, 1.87, 1.34, and 0.96 mg respectively after 6 days, while the developmental durations of such larvae were 16.3, 16.8, 17.5, 18.2, 19.5, and 21.2 days, respectively. Treatment with Bt affected the growth of the larvae at all instars (from the first to the fifth one). Through the comprehensive interference index of population control (CIIPC), the GM was calculated and the percentages were 30.4, 50.3, 63.8, 77.2, and 90.6% for the six tested concentrations respectively. Thus, the GM can be used to evaluate the efficiency of biological pesticides in agricultural practices in the future.