Mating disruption reduces the risk of resistance development to transgenic apple orchards: simulations of the lightbrown apple moth.
Computer simulations were used to determine the effect of interactions between apple trees expressing Bacillus thuringiensis-toxin and mating disruption on resistance evolution in Epiphyas postvittana. In transgenic orchards, it was assumed that 22% of the population was in the understorey and not subject to selection. Increasing expression of the toxin so that mortality increased from 90 to 99.99%, reduced the resistance allele frequency after 1000 days from 82% to zero. When 11% of the simulated orchards were replaced with wild, nontransgenic habitat (external refuge), the resistance allele frequencies declined compared to stimulations without the external refuge. The reduction was greatest when the expression of toxin was highest. Mating disruption always reduced the resistance allele frequency. When the expression of the Bt-toxin gene killed 90% of susceptible individuals, the resistance allele frequency was 82% after 1000 days, but 61.4% with 10% mating disruption, and 0.154% with 90% mating disruption (the initial resistance allele frequency was 0.1%). Mating disruption decreased the size of the treated population and increased the relative effect of immigration from refugia.