Interactions of entomopathogens with insect growth regulators for the control of Spodoptera littoralis (Lepidoptera: Noctuidae)

Abstract

Agriculture is currently expected to establish different pest insect control alternatives that have less impact and involve a lower environmental risk. New legislative regulations on the use of plant protection products give priority to biological control measures over the use of chemical insecticides. One of the potential control alternatives to be included in integrated pest management is the combination or simultaneous use of chemical agents, in low doses, with insecticides of microbial origin, seeking to maximize their potential and at the same time reduce the environmental impact that chemical control can cause. This work evaluates the effects of three microbial agents to control Spodoptera littoralis: Bacillus thuringiensis var. aizawai; a native isolate of Beauveria bassiana; and the S. littoralis nucleopolyhedrovirus (SlNPV). These have been used both as individual treatments and in combination with low doses of lufenuron and tebufenozide, synthetic compounds that act as Insect Growth Regulators (IGRs). The median lethal concentrations (LC50) of SlNPV, lufenuron, and tebufenozide on third instar S.littoralis larvae were 6.6 × 105 OB/ml, 0.26 mg a.i./L, and 13.92 mg a.i./L, respectively. The results of simultaneous treatments showed additive effects for B. thuringiensis and B. bassiana with each of the IGRs tested. An antagonistic effect occurred when SlNPV and tebufenozide were administered simultaneously. In contrast, the combination of SlNPV and lufenuron resulted in a significantly higher larval mortality rate than treatments using each agent alone. It is concluded that simultaneous applications of these entomopathogens together with low concentrations of the IGRs can be included in Integrated Pest Management (IPM) programmes, exception of the combination SlNPV and tebufenozide. A product based on lufenuron and the SlNPV is presented as a potential candidate for commercial development.