Impact of violated high-dose refuge assumptions on evolution of Bt resistance.
Transgenic crops expressing Bacillus thuringiensis (Bt) toxins have been widely and successfully deployed for the control of target pests, while allowing a substantial reduction in insecticide use. The evolution of resistance (a heritable decrease in susceptibility to Bt toxins) can pose a threat to sustained control of target pests, but a high-dose refuge (HDR) management strategy has been key to delaying countervailing evolution of Bt resistance. The HDR strategy relies on the mating frequency between susceptible and resistant individuals, so either partial dominance of resistant alleles or nonrandom mating in the pest population itself could elevate the pace of resistance evolution. Using classic Wright-Fisher genetic models, we investigated the impact of deviations from standard refuge model assumptions on resistance evolution in the pest populations. We show that when Bt selection is strong, even deviations from random mating and/or strictly recessive resistance that are below the threshold of detection can yield dramatic increases in the pace of resistance evolution. Resistance evolution is hastened whenever the order of magnitude of model violations exceeds the initial frequency of resistant alleles. We also show that the existence of a fitness cost for resistant individuals on the refuge crop cannot easily overcome the effect of violated HDR assumptions. We propose a parametrically explicit framework that enables both comparison of various field situations and model inference. Using this model, we propose novel empiric estimators of the pace of resistance evolution (and time to loss of control), whose simple calculation relies on the observed change in resistance allele frequency.
Laboratoire Évolution, Génome et Spéciation CNRS UPR 9034 Unité de Recherche IRD 072 Gif-sur-Yvette France; Université Paris-Sud 11 OrsayFrance; Department of Ecology, Evolution & Natural Resources School of Environmental & Biological Sciences Rutgers University New Brunswick NJ USA; Noctuid Stem Borers Biodiversity in Africa Project Environmental Health Division International Centre for Insect Physiology & Ecology Nairobi Kenya; Institute of Integrative Biology University of Liverpool Liverpool UK.
Pascal
P
Campagne
Department of Ecology, Evolution & Natural Resources School of Environmental & Biological Sciences Rutgers University New Brunswick NJ USA.
Peter E
PE
Smouse
Laboratoire Évolution, Génome et Spéciation CNRS UPR 9034 Unité de Recherche IRD 072 Gif-sur-Yvette France; Université Paris-Sud 11 Orsay France; Noctuid Stem Borers Biodiversity in Africa Project Environmental Health Division International Centre for Insect Physiology & Ecology Nairobi Kenya.
Rémy
R
Pasquet
Laboratoire Évolution, Génome et Spéciation CNRS UPR 9034 Unité de Recherche IRD 072 Gif-sur-Yvette France; Université Paris-Sud 11 Orsay France.
Jean-François
JF
Silvain
Laboratoire Évolution, Génome et Spéciation CNRS UPR 9034 Unité de Recherche IRD 072 Gif-sur-Yvette France; Université Paris-Sud 11 Orsay France; Noctuid Stem Borers Biodiversity in Africa Project Environmental Health Division International Centre for Insect Physiology & Ecology Nairobi Kenya.
Bruno
B
Le Ru
School of Biological Sciences - Zoology North-West University Potchefstroom South Africa.
Johnnie
J
Van den Berg
fitness cost; high‐dose; incomplete resistance; insecticide resistance; nonrandom mating; partial dominance; refuge strategy