Are feeding preferences and insecticide resistance associated with the size of detoxifying enzyme families in insect herbivores?

• Compared detoxification gene families (P450s, CCEs, GSTs) across 65 insect genomes.
• Two to four fold differences in the number of these genes between species.
• The sizes of these gene families correlate in most insect orders compared.
• These sizes also correlate with feeding preference in some orders.
• Still unclear whether there is an independent correlation with insecticide resistance.

The size of gene families associated with xenobiotic detoxification in insects may be associated with the complexity of their diets and their propensities to develop insecticide resistance. We test these hypotheses by collating the annotations of cytochrome P450, carboxyl/cholinesterase and glutathione S-transferase genes in 65 insect species with data on their host use and history of insecticide resistance. We find 2–4 fold variation across the species in the numbers of these genes and, in some orders, especially the Hymenoptera, there is a clear relationship between the numbers of genes and feeding preferences. However in other orders, in particular the Lepidoptera, no such relationship is apparent. The size of these three gene families also tend to correlate with insecticide resistance propensity but this may not be an independent effect because species with broader host ranges are more likely to be pests that are heavily sprayed with insecticides.