Effects of Bacillus thuringiensis var. kurstaki and Spinosad on three larval stages 1st, 2nd and 3rd of tomato borer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in laboratory conditions

The tomato borer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is considered to be one of the most devastating pests affecting the tomato crops, where crop losses range from 60 to 100%. In this research, two bio-insecticides, Bacillus thuringiensis and Spinosad, were evaluated for their efficacy in the control of T. absoluta , on tomato plant in a laboratory conditions. The LC ₂₅ and LC ₅₀ values of B. thuringiensis and Spinosad were estimated on larval instars 1st, 2nd and 3rd. Furthermore, LC ₅₀ values for B. thuringiensis treatments on three larval stages were 2386.755, 2109.978 and 2757.651 ppm and for Spinosad 1283.915, 1339.862 and 2253.188 ppm, respectively, and LC ₂₅ values of B. thuringiensis and Spinosad treatments on three larval stages were 985.440, 1368.202 and 1914.574 ppm and 436.268, 643.788 and 1526.941 ppm, respectively. After determining the LC ₅₀ and LC ₂₅ values of both agents, to evaluate the combined effects of bacterium and Spinosad, an experiment was conducted in the form of completely randomised design with four treatments including LC ₅₀ (Bt), LC ₅₀ (Sp), LC ₂₅ (Bt) plus LC ₂₅ (Sp) and control. Statistical analysis of the results showed that percentage mortality combination of two biological agents treatment on three larval stages 1st, 2nd and 3rd of T. absoluta compared with control, Spinosad and B.t alone treatments have significant differences (P < 0.05). Our results demonstrated that Spinosad was more effective in the control of T. absoluta lethality, than the B. thuringiensis treatment. The LC ₂₅ and LC ₅₀ values of B. thuringiensis and Spinosad were demonstrated on three larval stages in which first instar larvae was the most susceptible. The results showed that the combination of B. thuringiensis and Spinosad have good additive effect when compared with applied individually treatments. We recommend the combination of two biological agents to control this pest. Our current study indicated that the concept of integrating bio-insecticides, B. thuringiensis and Spinosad, with other control tactics, especially with environmentally acceptable agents has opened further opportunities for their uses as biological control agents of insect pest.