Joint Action of Bacillus thuringiensis kurstaki and Nuclear Polyhedrosis Virus Against Spodoptera littoralis (Lepidoptera, Noctuidae)

AbsractIntroduction: Synthetic chemical insecticides are becoming ineffective against Spodoptera littoralis (Boisaduval, ۱۸۳۳) because of resistance. Microbial insecticides, also known as entomopathogens, are an effective and environmentally acceptable way to control insect pests.Methods: Bacillus thuringiensis kurstaki (Btk) and Nuclear Polyhedrosis Virus (NPV), either separately or in combination, were tested in the present investigation by exposing two field strains of S. littoralis under controlled laboratory conditions.Results: The NPV and Btk demonstrated high effectiveness toward larvae of both two field strains in a dose-dependent manner in terms of larval mortality recorded after ۳, ۵, and ۷ days. NPV appeared to be slightly more effective than Btk. In all cases, Btk combined with NPV-۱ (۱x۱۰ PIBs/mL) or NPV-۲ (۱x۱۰۷ PIBs/mL) had additive effects against larvae of either field strain. Combining Btk with NPV-۲ at concentration of ۳.۲x۱۰ IU/mL resulted in significant synergism against larvae of either of the two field strains examined. When larvae were fed Btk and NPV-contaminated leaf discs, their growth and pupation rates were reduced.Conclusions: The results showed that the NPV and Btk could be fine as microbial insecticides when mixed to control and manage the insecticide-resistant S. littoralis in the field.