Schoville, S. D. | Search bioRxiv

bioRxiv2017

A model species for agricultural pest genomics: the genome of the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

The Colorado potato beetle is one of the most challenging agricultural pests to manage. It has shown a spectacular ability to adapt to a variety of solanaceaeous plants and variable climates during its global invasion, and, notably, to rapidly evolve insecticide resistance. To examine evidence of rapid evolutionary change, and to understand the genetic basis of herbivory and insecticide resistance, we tested for structural and functional genomic changes relative to other arthropod species using genome sequencing, transcriptomics, and community annotation. Two factors that might facilitate rapid evolutionary change include transposable elements, which comprise at least 17% of the genome and are rapidly evolving compared to other Coleoptera, and high levels of nucleotide diversity in rapidly growing pest populations. Adaptations to plant feeding are evident in gene expansions and differential expression of digestive enzymes in gut tissues, as well as expansions of gustatory receptors for bitter tasting. Surprisingly, the suite of genes involved in insecticide resistance is similar to other beetles. Finally, duplications in the RNAi pathway might explain why Leptinotarsa decemlineata has high sensitivity to dsRNA. The L. decemlineata genome provides opportunities to investigate a broad range of phenotypes and to develop sustainable methods to control this widely successful pest.

genomics↗

bioRxiv2017

Origin of pest lineages of the Colorado potato beetle, Leptinotarsa decemlineata

Colorado potato beetle (Leptinotarsa decemlineata Say) is a pest of potato throughout the Northern Hemisphere, but little is known about the beetles origins as a pest. To determine the origins of pest populations of CPB, we sampled the beetle from uncultivated Solanum host plants in Mexico, and from pest and non-pest populations in the U.S. We used mtDNA and nuclear loci to examine three hypotheses on the origin of the pest lineages: 1) the pest beetles originated from Mexican populations, 2) the pest beetles descended from hybridization between previously divergent populations, or 3) the pest beetles descended from populations that are native to the Plains states in the United States. We examined patterns of genetic diversity among geographic regions in order to detect invasion-related genetic information. Mitochondrial haplotypes of non-pest populations from Mexico and southern Arizona differed substantially from beetles collected from the southern plains and potato fields in the U. S., indicating that beetles from Mexico and Arizona did not contribute to founding the pest lineages. Similar results were observed for AFLP and microsatellite data. In contrast, non-pest populations from the southern plains of Colorado, Kansas, Nebraska, New Mexico, and Texas were genetically similar to U. S. pest populations, clearly indicating that they contributed to the founding of the pest lineages. Although some pest populations are less genetically diverse (e.g., Washington, Idaho), most of the pest populations do not show a significant reduction in genetic diversity compared to the plains populations in the U. S. In contrast to the colonization patterns typical of exotic pests, our analyses suggests that a large genetically heterogeneous beetle populations expanded onto potato from native Solanum hosts. As an endemic colonization of a novel host plant, this host range expansion may have contributed to the relatively abundant genetic diversity of contemporary populations, perhaps contributing to the rapid evolution of host range and insecticide resistance in this widely successful insect pest.

evolutionary biology↗