Invasion of Trichoferus campestris (Coleoptera: Cerambycidae) into the United States characterized by high levels of genetic diversity and recurrent introductions

Genetic variability of invasive pests informs us of fundamental aspects of the invasion, which help leverage limited resources for more efficient pest management. This is particularly important for managing species with invasive populations fueled by recurrent introductions. We present the first phylogeographic study of the velvet longhorned beetle (Trichoferus campestris [Faldermann]), a highly polyphagous wood-boring insect native to Asia. It attacks many ecologically and economically important tree species and has repeatedly invaded Europe and North America in recent decades. Despite the apparent threat posed by this pest, little work has been attempted to characterize genetic variability of T. campestris. One hurdle is the lack of genetic data beyond the “universal” COI barcode. Here we designed primer sequences to amplify five additional mitochondrial protein-coding genes for T. campestris (COII, COIII, Cytb, ND2, and ND4). We included specimens collected from domestic locations in the Unites States (U.S.) as well as samples intercepted in solid wood packaging material (WPM) at U.S. ports of entry. Phylogenetic analyses recovered three mitochondrial lineages, all including both domestic collections and port-interceptions. Our results demonstrated high levels of haplotype diversity among invasive populations of T. campestris. Specimens collected from the same geographical vicinity can be placed into different lineages. Species delimitation analyses further suggest presence of multiple molecular operational taxonomic units, which could complicate regulatory policies. We evaluated mechanisms that underlie the increasing number of T. campestris individuals and populations detected in the U.S. Results support the hypothesis of independent introductions through WPM, but are inconsistent with secondary invasions through the bridgehead effect.