Determinants of host breadth in non-native bark and ambrosia beetles

Most phytophagous insects are specialists, so availability of suitable host plants often may be a critical factor limiting establishment of non-native insect species. Here we investigate the extent to which established non-native tree-feeding insects utilize hosts that are native to the invaded range as well as hosts that are themselves non-native. We accomplish this by comparing host use among all native and non-native bark beetles and pinhole borers (Scolytinae and Platypodinae) established in Europe and North America reported in the literature. These groups of insects are well-known for the disparity among species in specialized behavior and development tied to host physiology. We find considerable variation in host breadth, as measured by species-level and genus-level host richness and phylogenetic diversity of hosts, among different feeding guilds (ambrosia beetles, true bark beetles, twig beetles, and others). In each region, ambrosia and twig beetles exhibit the greatest diversity of hosts. Host breadth on native plants was generally greater for native beetle species than for non-native beetle species. In contrast, host breadth of non-native beetles is generally greater on non-native plants than on plants native to the focal region. These results indicate that successful invasion of these insect herbivores is dependent on the prior introduction of their non-native host plants, or the availability of native hosts that are closely related to their ancestral host plants.