Abstract
The “High Dose/Refuge” strategy (HD/R) is the currently recommended Insect Resistance Management strategy (IRM) to limit resistance development to Bacillus thuringiensis (Bt) plants. This strategy requires planting a “refuge zone” composed of non-Bt plants suitable for the target insect and in close proximity to a “Bt zone” expressing a high toxin concentration. One of the main assumptions is that enough susceptible adults mate with resistant insects. However, previous studies have suggested that the high toxin concentration produced by Bt plants induces slower insect development, creating an asynchrony in emergence between the refuge and the Bt zone and leading to assortative mating between adults inside each zone. Here, we develop a deterministic model to estimate the impact of toxin concentration, emergence asynchrony and refuge zone size on the effectiveness of the HD/R strategy. We conclude that emergence asynchrony only affects resistance when toxin concentration is high and resistance is recessive. Resistance develops more rapidly and survival of susceptible insects is higher at lower toxin concentration, but in such situations, resistance is insensitive to emergence asynchrony.
Highlights
Chemical pesticides have been powerful tools for insect pest control for over 4000 years, but they can have numerous negative impacts, such as mortality of nontarget species, and contamination of aquatic and terrestrial environments and human or animal food
Bacillus thuringiensis (Bt)-based formulations have several limitations: (1) their specificity is a problem if several pests simultaneously attack the same crop; (2) in comparison with synthetic pesticides, the target insect dies later; (3) toxin persistence is limited in the field and (4) the Bt spray cannot reach mining insects [1,6,7]
In 2010, 63% of the corn plants in the United States were transgenic insecticidal hybrids [9]. Such a constant exposure of large pest populations to Bt plants increases the risk of resistance development, which could limit the efficacy of Bt plants and, more broadly, the application of effective and authorized microbial pesticides in biological agriculture [6]
Summary
Chemical pesticides have been powerful tools for insect pest control for over 4000 years, but they can have numerous negative impacts, such as mortality of nontarget species, and contamination of aquatic and terrestrial environments and human or animal food To mitigate such negative impacts, alternative methods of pest control have been sought and implemented, including biological control agents, pheromones, insect growth regulators, genetic manipulation of pest species, host-plant resistance, and microbial pest control [1,2,3]. Ninety-five percent of microbial pesticides are composed of Bacillus thuringiensis (Bt) [4], a Gram positive bacterium producing insecticidal toxins (Cry toxins) during its sporulation [5] These biological pesticides are specific (harmless for nontarget insects, fish, birds, mammals and humans), are produced at industrial scales, and require standard equipment for application. Such a constant exposure of large pest populations to Bt plants increases the risk of resistance development, which could limit the efficacy of Bt plants and, more broadly, the application of effective and authorized microbial pesticides in biological agriculture [6]
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