The Mexican potato beetle? Phylogeographic insights into the historical expansion of Leptinotarsa decemlineta.

Leptinotarsa decemlineata, the Colorado potato beetle is considered the most important insect pest of Solanum tuberosum, the common potato, within the Northern hemisphere (Hare 1990) . L. decemlineata is thought to originate from the central highlands of Mexico where ancestral populations feed exclusively upon wild solanaceous species, including Solanum angustifolium, Solanum elaeagnifolium, and Solanum rostratum. Previous molecular evidence supports the hypothesis of post-colonization evolution within derived populations of L. decemlineata. Despite the previous molecular studies regarding the population genetics of L. decemlineata, there still remains little genetic information regarding the ancestral region of the beetle. As a result, any broad conclusions regarding the history of the L. decemlineata expansion and the relationship between ancestral and derived populations are likely to be incomplete and possibly inaccurate. To provide a clearer picture of this historic expansion and the genetic associations between the ancestral and derived populations of L. decemlineata, our study investigates the population structure and genetic variability of Mexican and USA populations of the beetle throughout its North American distribution. Using MtDNA sequence data, AFLPs and microsatellite analyses we identified significant divergences among ancestral (Mexican) and derived (USA) populations. Our results help to clarify the natural history of the Colorado potato beetle and the conditions leading to its expansion.