Tolerance and cross-tolerance to emamectin benzoate and group 28 insecticides in filed and laboratory population of diamondback moth Plutella xylostella.

Improvements in synthetic and biological insecticides and their over-use has led to wide spread resistance in field insect pests with the emergence of new resistance and/or tolerance mechanisms. We previously reported that sub-lethal exposure to insecticides can lead to development of tolerance in different lepidopteran insect larvae, with the potential for further development of genetic resistance.

In this study we have demonstrated that some field populations of diamondback moth Plutella xylostella (L.) have now developed significant levels of tolerance to two important groups of newer insecticides (IRAC Groups 6 and 28), and that these tolerance levels are already capable of reducing the field control achieved with these Group 6 and 28 insecticides. We also found that high levels of tolerance can result in the laboratory from repeated exposure to low concentrations of synthetic (eg. Group 6 insecticide emamectin benzoate) or microbial (eg. Bacillus thuringiensis var. kurstaki) insecticide. Our data suggest that at early stages the acquisition of this tolerance through a novel inducible tolerance mechanism, but as the selection process progressed, a combination of induced metabolic tolerance and genetic mutation(s) were found to contribute to the overall tolerance and/or resistance. Further, the P. xylostella laboratory selected strain which has acquired high level of tolerance to emamectin benzoate is exhibiting cross-tolerance to Group 28 diamides insecticides. Studies are underway to identify the molecular basis of the observed tolerance and cross-tolerance, and to determine the full implications of the inducible tolerance process to resistance management.