A chromosome-scale genome assembly of the pollen beetle, Brassicogethes, provides insight into cytochrome P450-mediated pyrethroid resistance

The pollen beetle, Brassicogethes aeneus, is an economically important pest of oilseed rape (Brassica napus) throughout Europe. The control of B. aeneus has relied heavily on the use of chemical insecticides leading to the evolution of resistance. However, investigation of the molecular basis of resistance has been hampered by an absence of genomic resources for this species, including the lack of a reference genome assembly. Here we address this need by generating a chromosome-scale genome assembly for B. aeneus. A combination of long-read single-molecule sequencing and in vivo chromatin conformation capture (Hi-C) sequencing was used to generate an assembly of 585 Mb, comprising 11 chromosome sized scaffolds (scaffold N50 of 61.6 Mb) and containing 13,381 protein-coding genes. We leveraged the new assem- bly, in combination with post-genomic functional approaches to investigate the molecular basis of metabolic resistance to pyrethroid insecticides in B. aeneus. Our data confirmed that two P450s, CYP6BQ23 and CYP6BQ25, have the capacity to metabolise the pyrethroid deltamethrin in B. aeneus and thus have the potential to confer resistance. However, the relative expression of these P450s in pyrethroid susceptible and resistant strains suggests that CYP6BQ23 plays a much more significant role in resistance than CYP6BQ25. In summary, the high-quality genome assembly for B. aeneus reported here provides a valuable resource for future research on this species. Our findings on P450-mediated resistance to insecticides are of applied relevance for the development of strategies for the sustainable control of this important pest.