Interaction effects of Bacillus thuringiensis subsp. kurstaki and single nuclear polyhedrosis virus on Plutella xylostella

Abstract

The interaction effects of Bacillus thuringiensis subsp. Kurstaki and HaSNPV on the survival of second instars of Plutella xylostella were evaluated under laboratory conditions. The exposure of second instars to the combination of HaSNPV (2.3×103, 3.8×104, 6.6×105 occlusion bodies (OB) ml−1) and B. thuringiensis subsp. kurstaki (2.4×101, 3.4×103, 4.7×105 spores ml−1), indicated an additive effect in the toxicity of most combinations. Synergism occurred when the lowest concentration of the combination of B. thuringiensis (2.4×10−1 spores ml−1) and HaSNPV (2.3×103 OB ml−1) was applied. When the larvae were fed on leaf discs contaminated with both B. thuringiensis and HaSNPV, their growth and developmental rates were decreased and a reduction in their pupation rate, pupal weight as well as the emergence rate of adults was observed. The LT50 values correlated negatively with B. thuringiensis and HaSNPV concentrations.