Selection for Cry3Bb1 resistance in a genetically diverse population of nondiapausing western corn rootworm (Coleoptera: Chrysomelidae).

Five short-diapause laboratory lines of western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), were selected for resistance to MON863, a variety of corn genetically modified with the Bacillus thuringiensis Berliner (Bt) transgene that expresses the Cry3Bb1 delta-endotoxin. Three of the selected lines were developed by incremental increase in the duration of exposure to MON863 over 11 generations (moderate selected lines). Two selected lines were developed from a control group by constant exposure to MON863 for at least 14 d posthatch over seven generations (intense selected lines). At the end of the experiment, survivorship, as measured by adult emergence, was approximately 4 times higher in each of the selected lines reared on MON863 compared with control lines. Estimates of realized heritabilities (h2) were 0.16 and 0.15 for the moderate and intense selected lines, respectively, and are consistent with h2 estimates reported previously from a variety of pest insects. These lines provide data necessary for evaluating the potential for Bt resistance within diabroticite beetles and will be useful for developing improved insect resistance management strategies.

Cytonuclear patterns of genetic diversity and the intricate evolutionary history of the inland silverside (Menidia beryllina).

DNA sequence variation at a mitochondrial and a nuclear intron locus was surveyed within and among multiple populations of the inland silverside (Menidia beryllina) from the southeastern United States and revealed discordant phylogenetic patterns but similar patterns of population genetic variation across nuclear and mitochondrial loci. Mitochondrial variation was geographically structured, with strongly supported monophyletic assemblages among Gulf of Mexico population samples and a close association of the St John's River (SJ) population with these same samples. Nuclear alleles were not strongly structured geographically, with little support for monophyly within or across basins. Conversely, population genetic parameters indicate that the bulk of genetic diversity for both genomes resides within and among Gulf of Mexico populations and that diversity within the Atlantic is largely restricted to the SJ population. The contrast in genetic variation and population phylogenies appears to be a function of historical demographic processes, most likely directed by fluctuating geomorphology of the Florida peninsula in response to North American glaciation cycles.