Diamondback moth resistance to Bacillus thuringiensis transgenic canola: evaluation of refugia size with non‐recessive resistant insects

Abstract

Abstract: Current recommendations to delay the evolution of resistance to Bacillus thuringiensis crops are that a minimum of 5–50% of a crop‐growing region should include non‐B. thuringiensis varieties as refuges. These recommendations are based in part on the assumption that resistance will be inherited as a recessive trait. Laboratory microcosm experiments are described with transgenic canola expressing Cry1Ac and a non‐recessive Cry1Ac resistant population of the diamondback moth Plutella xylostella, in which the effect of different sizes of refugia (0%, 20% and 50%) on resistance was compared over five generations. The LC50 values for Cry1Ac increased markedly in the P. xylostella sub‐populations with 0% (>100‐fold) and 20% refugia (>35‐fold) but showed little change (less than fivefold increase) with 50% refugia. The results support the idea that relatively high levels of refugia (non‐B. thuringiensis varieties) may be required where resistance is not functionally recessive at the level of toxin expressed in the B. thuringiensis crop.