Insights into the evolution of beetle Cytochrome P450's from the genomes of Harmonia axyridis (Coccinellidae) and Tribolium castaneum (Tenebrionidae)

Our knowledge of beetle Cytochrome P450 (CYP) genes comes mostly from studies of the model beetle and grain pest Tribolium castaneum. To gain additional insight into beetle CYPs and ultimately to inform our understanding of beetle CYP evolution, we identified and annotated all CYP genes present in a new draft genome of Harmonia axyridis, the Asian multicolored ladybug. Harmonia axyridis is a voracious predator of other insects and an important biological control agent. It also carries toxic secondary metabolites in its hemolymph that are a component of reflex bleeding. Overall, we identified somewhat fewer CYPs in H. axyridis (nearly 100) than are known from T. castaneum (137 plus 2 slight variants and 10 pseudogenes). A phylogeny of the CYPs from these species illustrates the presence of CYP "blooms" in T. castaneum that are lacking in H. axyridis. Several additional CYPs are present in H. axyridis but missing from T. castaneum. Sequence similarity statistics further suggest that certain of the H. axyridis CYP genes are relatively more plesiomorphic than those in T. castaneum. Interestingly, both species carry CYP4G genes, which are candidates for resistance to insecticides, including permethrins. While it is likely that a few CYP genes remain to be identified in the H. axyridis genome, our ongoing work indicates that the vast majority have been identified. Consequently, the relatively small number of CYPs present in H. axyridis (relative to T. castaneum) is real. We are now expanding this work to include studies of the CYPs present in several additional beetle species in the hope of gaining further insight into the evolution of beetle CYP genes.