Abstract
Over the past decade, the high-dose refuge (HDR) strategy, aimed at delaying the evolution of pest resistance to Bacillus thuringiensis (Bt) toxins produced by transgenic crops, became mandatory in the United States and is being discussed for Europe. However, precopulatory dispersal and the mating rate between resident and immigrant individuals, two features influencing the efficiency of this strategy, have seldom been quantified in pests targeted by these toxins. We combined mark-recapture and biogeochemical marking over three breeding seasons to quantify these features directly in natural populations of Ostrinia nubilalis, a major lepidopteran corn pest. At the local scale, resident females mated regardless of males having dispersed beforehand or not, as assumed in the HDR strategy. Accordingly, 0–67% of resident females mating before dispersal did so with resident males, this percentage depending on the local proportion of resident males (0% to 67.2%). However, resident males rarely mated with immigrant females (which mostly arrived mated), the fraction of females mating before dispersal was variable and sometimes substantial (4.8% to 56.8%), and there was no evidence for male premating dispersal being higher. Hence, O. nubilalis probably mates at a more restricted spatial scale than previously assumed, a feature that may decrease the efficiency of the HDR strategy under certain circumstances, depending for example on crop rotation practices.
Highlights
Right after emergence and just before mating, adult insects face a crucial dilemma that The Clash [1] celebrated in a famous song that could be slightly rephrased as: ‘‘Should I mate or should I go now? If I mate there will be trouble
Our results show that immigrant males, once present locally, have the same probability of mating with resident females as resident males have, while limited evidence suggests that immigrant females mate less readily with local males than do resident females
European corn borer (ECB) larvae having overwintered in these 2003 cornfields were the closest, and the most likely, sources of wild moths occurring at the study sites in 2004
Summary
Right after emergence and just before mating, adult insects face a crucial dilemma that The Clash [1] celebrated in a famous song that could be slightly rephrased as: ‘‘Should I mate or should I go now? If I mate there will be trouble. The timing between mating and dispersal is likely to vary with species and environmental conditions [2]: in the absence of a universal optimal strategy, no general prediction can be made and each species of interest must be studied on its own. The timing between mating and dispersal can be of great practical importance: notably, it may influence the efficacy of strategies intended to drive the microevolution of agricultural pest species—e.g., the evolution of their resistance to control agents such as pesticides—by managing agricultural landscapes [3]. The ‘‘high-dose refuge’’ (HDR) strategy [4] is one such strategy. It is aimed at delaying or preventing the evolution of resistance in target pest populations against Bacillus thuringiensis (Bt) toxins produced by transgenic Bt crops [5]. An HDR-based management of agricultural land became mandatory for several Bt crops in the United States [5] and is being discussed for Europe [7]
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