Biochemical Basis of Synergism between Entomopathogens and Insecticide Spinetoram against Plutella xylostella (L.)

Abstract

Increasing incidences of insecticide resistance in diamondback moth Plutella xylostella (L.), the most ravaging pest of cruciferous vegetables, have stimulated interest in alternative pest management strategies. In this study, we have developed a spinetoram-resistant population of P. xylostella and examined the single and combined toxicity of Bacillus thuringiensis subsp. kurstaki and Beauveria bassiana with spinetoram. Additionally, enzyme activities were tested to study the influence of biopesticides in the mitigation of detoxifying enzymes. P. xylostella has developed high level of resistance (174.06-fold) against spinetoram after 16 generations of selection. B. thuringiensis subsp. kurstaki and B. bassiana exhibited high toxicity to spinetoram-resistant population of P. xylostella. Synergism was observed between B. thuringiensis subsp. kurstaki + spinetoram and B. bassiana + spinetoram with co-toxicity factor of 30.23 and 22.51, respectively. The joint application of spinetoram + B. bassiana and spinetoram + B. thuringiensis subsp. kurstaki resulted in suppression of mixed-function oxidase activity by 7.93 to 9.23 per cent and carboxyl-esterase activity by 5.64 to 6.18 per cent. Mixtures of biopesticides with spinetoram exhibited synergistic effects and may aid the design of new combinations of management strategies to delay resistant development in P. xylostella.