Host polyphagy in insects is hypothesized to be associated with a greater gene repertoire in gene families directly or indirectly involved in xenobiotic detoxification or sensing. Here we test this hypothesis by focussing on 58 species and nine such gene families which includes the highest numbers of genes ever reported in insects for the eight families. To do so we created a novel orthology pipeline that was able to sensitively identify increased conservation as tested in Drosophila species while identifying lineage specific gene expansions across the genome. The workflow to study the 58 species was therefore based on duplication and orthology sensitive characterisation of gene families. We found that polyphagous species had more genes and especially duplications when compared with restricted specialists from the same insect order. Species feeding on leaf tissues and seeds which were expected to represent the most toxic diets had particularly broad gene repertoires. These patterns were mainly driven by P450, CCE, ABC transporter and OBP gene families and their detoxification sub-classes, with OBPs being present in lower numbers in the five most aggressive polyphagous pest species considered in the study. The data suggest a strong biological signal for evolution of polyphagy and/or tolerance of toxic diets.