Toxicity of Bacillus thuringiensis var. kurstaki and Spinosad on three larval stages of beet armyworms Spodoptera exigua (Hübner) (Lep: Noctuidae)
Abbas Hosseinzadeh and Shahram Aramideh
The beet armyworm, Spodoptera exigua (Hübner), is a polyphagous pest that causes serious damages to various plants including beet, potato and cotton. In order to reduce application of chemical insecticides, two bioinsecticides, Bacillus thuringiensis and Spinosad, were evaluated for their efficacy in control of S. exigua in laboratory conditions. The LC25 and LC50 values of B. thuringiensis and Spinosad were estimated on three larval stages. Furthermore, LC50 values for B. thuringiensis treatments on 1st, 2nd and 3rd larval stages were 275. 305, 717.444 and 727.671 ppm and for Spinosad 276.715, 521.058 and 568. 914 ppm, respectively, and LC25 values of B. thuringiensis and Spinosad treatments on 1st, 2nd and 3rd larval stages were 104.105, 341.652 and 441.803 ppm and 92.812, 369.569 and 379.958 ppm, respectively. After determining the LC50 and LC25 values of both agents, to evaluate their combined effects, an experiment of completely randomized design was conducted with four treatments including LC50 (Bt), LC50 (Sp), LC25 (Bt) + LC25 (Sp) and control. Statistical analysis of the results showed that mortality percentage of two biological control combination on three larval stages 1st, 2nd and 3rd of S. exigua have significant differences (P<0.05) in comparition to control, Spinosad and B.t alone treatments. These results demonstrated that Spinosad was more effective in control of S. exigua, than B. thuringiensis. Thus our recommendation is the combination of two biological agents to control of beet armyworm.
Abbas Hosseinzadeh, Shahram Aramideh. Toxicity of Bacillus thuringiensis var. kurstaki and Spinosad on three larval stages of beet armyworms Spodoptera exigua (Hübner) (Lep: Noctuidae). J Entomol Zool Stud 2016;4(5):375-379.