Population genetics of Chrysomela tremulae: a first step towards management of transgenic Bacillus thuringiensis poplars Populus tremula X P-tremuloides

Many strategies have been proposed for delaying the development of insect r esistance to Bacillus thuringiensis (Bt). The current paradigm for Bt resis tance management is the high dose-refuge strategy. For this strategy to be successful: (i) heterozygotes must be killed in treated areas, (ii) resista nt alleles must be rare (frequency < 10-3), and (iii) there must be a high level of gene flow between populations to ensure random mating. We studied gene flow within and between populations with a view to managing the resist ance of Chrysomela tremulae (Coleoptera: Chrysomelidae) to new transgenic, highly toxic poplars expressing a synthetic Br gene. In this study, we asse ssed the extent of gene flow in C. tremulae within and between 16 sites in France and Belgium, using allozyme markers. We found a high level of geneti c variability in C, tremulae, with a mean of 0.206<plus/minus>0.16. There w ere no obvious limitations to gene flow between populations of C. tremulae over large geographical distances (several hundreds of kilometres). Neverth eless, a very low level of genetic differentiation was observed between a s ite located in the south of France and the sampled sites from the Centre re gion.