Efficacy of entomopathogenic nematodes and Bacillus thuringiensis against diamondback moth Plutella xylostella (L.)

A study was undertaken to determine efficacy and interaction between entomopathogenic nematodes and Bacillus thuringiensis var. kurstaki against 2nd and 3rd larval instars of diamondback moth (DBM) Plutella xylostella (DBM) under laboratory conditions. Mortality of 2nd instar larvae to Steinernema abbasi was between 73.33 and 100 per cent using the concentrations between 50 and 250 Ijs/ml. The 3rd instar larvae showed mortality percentages between 66.66 and 100 for the same concentrations, whereas mortality percentage for 2nd instar larvae to heterorhabditis indica was between 33.33 and 100 using concentrations between 50 and 500 Ijs/ml. With regard to 3rd larval instar, h. indica caused mortality between 23.33 and 86.67 per cent at concentrations between 50 and 1000 Ijs/ml. Among the two nematode species, S. abassi proved to be more effective than the h. indica. With regard to Bacillus thuringiensis (Bt) treatment, 100 per cent mortality was observed at 1000 μg/ml in 2nd instar larvae but in case of 3rd instar the larval mortality was 96.67 per cent. There was no improvement in the efficiency of the combination treatment over that of nematode or bacterium when each was used alone. Moreover, the observed mortality was less than the expected mortality, assuming independent action and indicating an antagonistic interaction. The additive or synergistic interaction between Bt and entomopathogenic nematodes may offer a powerful and reliable tool for DBM control.