La pyrale se disperse-t-elle suffisamment pour limiter durablement la résistance au maïs Bt via la stratégie « haute dose/refug

Abstract

The use of transgenic crops producing toxins from the bacterium Bacillus thuringiensis - or Bt crops - is associated with the risk that the targeted pests become resistant to these toxins. To reduce this risk, the US government required the implementation of a strategy named High Dose/Refuge (HDR). This strategy is based on maintaining Bt toxin-free plants or crops - referred to as « refuges » - to preserve a pool of susceptible insects in the vicinity of Bt fields. Among other factors, its efficiency relies on a high gene flow between these susceptible individuals and any resistant individuals selected in Bt fields. For several pests targeted by these toxins, this strategy was nevertheless implemented when little was in fact know, as to the life history traits likely to influence the intensity of the gene flow. Part of this gap has been filled since then: we summarize here the recent advances on the European corn borer (ECB), one of the main targets of insecticidal Bt maize. Although this moth pest is highly polyphagous, its other host plants - whether wild or cultivated - do not provide a sufficient source of susceptible individuals to efficiently prevent toxin resistance from developing. Moreover, a fraction of the ECB reproduce in close vicinity of their place of emergence, so that refuges situated a few hundred meters from Bt maize fields - the maximal distance currently required is 800 meters - may not warrant a sufficient intermixing between susceptible and resistant individuals. In crop rotation situations, this intermixing could however be facilitated through a contrasted management of herbaceous maize field borders. Although 10 years after the beginning of Bt maize cultivation no resistance has yet broken out, our data suggests that it is illusory to aim at a universally suitable strategy, and that the HDR strategy - as currently implemented - may not necessarily be optimal.