A de novo transcriptome of European pollen beetle populations and its analysis, with special reference to insecticide action and resistance.

The pollen beetle Meligethes aeneus is the most important coleopteran pest in European oilseed rape cultivation, annually infesting millions of hectares and responsible for substantial yield losses if not kept under economic damage thresholds. This species is primarily controlled with insecticides but has recently developed high levels of resistance to the pyrethroid class. The aim of the present study was to provide a transcriptomic resource to investigate mechanisms of resistance. cDNA was sequenced on both Roche (Indianapolis, IN, USA) and Illumina (LGC Genomics, Berlin, Germany) platforms, resulting in a total of ∼53 m reads which assembled into 43 396 expressed sequence tags (ESTs). Manual annotation revealed good coverage of genes encoding insecticide target sites and detoxification enzymes. A total of 77 nonredundant cytochrome P450 genes were identified. Mapping of Illumina RNAseq sequences (from susceptible and pyrethroid-resistant strains) against the reference transcriptome identified a cytochrome P450 (CYP6BQ23) as highly overexpressed in pyrethroid resistance strains. Single-nucleotide polymorphism analysis confirmed the presence of a target-site resistance mutation (L1014F) in the voltage-gated sodium channel of one resistant strain. Our results provide new insights into the important genes associated with pyrethroid resistance in M. aeneus. Furthermore, a comprehensive EST resource is provided for future studies on insecticide modes of action and resistance mechanisms in pollen beetle.