Construction and characterisation of near-isogenic Plutella xylostella (Lepidoptera: Plutellidae) strains resistant to Cry1Ac toxin

BACKGROUND Resistance to insecticidal Bacillus thuringiensis (Bt) toxins has arisen in multiple populations of the worldwide Brassica pest Plutella xylostella (L.). To help elucidate the mechanism of resistance to Bt Cry1Ac toxin in a population from Florida, two pairs of near‐isogenic lines (NILs) were developed. RESULTS NILs were generated using either backcross or recombinant inbred line methodologies and evaluated for near‐isogenicity with inter‐simple‐sequence‐repeat (ISSR) markers. Backcross line BC6F4 maintained a similar level of Cry1Ac resistance to parental strain DBM1Ac‐R (>5000‐fold) yet showed 98.24% genetic similarity to the susceptible parental strain DBM1Ac‐S. Single‐pair backcrosses between DBM1Ac‐S and BC6F4 revealed that Cry1Ac resistance was controlled by one recessive autosomal locus. BC6F4 exhibited high levels of cross‐resistance to Cry1Ab and Cry1Ah but not to Cry1Ca or Cry1Ie. CONCLUSION Near‐isogenic strains were constructed to provide a reliable biological system to investigate the mechanism of Cry1Ac resistance in P. xylostella. These data suggest that resistance to Cry1Ac, Cry1Ab and Cry1Ah is probably caused by the alteration of a common receptor not recognised by Cry1Ca or Cry1Ie. Understanding Bt toxin cross‐resistance provides valuable information to consider when developing pest control strategies to delay resistance evolution. © 2014 Society of Chemical Industry