Variation in host usage among geographic populations of Leptinotarsa decemlineata,the Colorado potato beetle

Insect herbivores can become extensive invaders if they are able to undergo host expansions onto widely-grown agricultural host plants. An important yet unresolved question is whether all herbivore populations are equally able to utilize new host plants or if populations may be geographically structured, that is only a subset has the potential to undergo a host range expansion and become widely invasive. We examined if derived and ancestral geographic populations of L. decemlineata or Colorado potato beetle, varied in host preference and performance on both wild (Solanum rostratum) and cultivated (Solanum tuberosum) host plants. Sampling from six different North American regions (3 ancestral and 2 derived), we performed two full-factorial experiments to test for differences in host preference, acceptance, and performance on S. rostraum and S. tuberosum. Our results reveal the development of new (cultivated) host associations within pest populations of L. decemlineata following its geographic expansion. Pest beetles (i.e., Vermont populations) discriminated less between host plants and grew faster than all other beetle population on both host species. The Vermont beetles also developed faster on leaves than all other populations. The greater general preference, acceptance, and performance of Vermont beetles on all host types underscores the virulence of the pest form of the beetle and may help to explain the absence of pest incidence within the ancestral regions of L. decemlineata.