Co-Occurrence of the Invasive Banded and European Elm Bark Beetles (Coleoptera: Scolytidae) in North America

The invasive European elm bark beetle, Scolytus multistriatus (Marsham), was detected in Massachusetts a century ago, and it now occurs throughout the continental United States and southern Canada. The Asian banded elm bark beetle, Scolytus schevyrewi Semenov, was discovered in the United States in 2003, and now occurs in 28 states and the province of Alberta, Canada. Although the indigenous populations of these two species are allopatric, the invasive populations are now sympatric in North America where they co-colonize elm (Ulmus spp.) trees. A large-scale survey of these two Scolytus species was conducted with baited funnel traps, Plexiglas panel traps, and Ulmus pumila L. trap logs. Sites (four per locality) were monitored around Sacramento, CA; Reno, NV; Ogden, UT; Newcastle, WY; and Fort Collins, CO (2006-2007), and Manhattan, KS, and Columbia, MO (both only in 2007). Trap catches of S. schevrewyi relative to both Scolytus species captured from all three trapping methods at each survey site were 90 and 89% in Colorado, 90 and 83% in Wyoming, 60 and 68% in Utah, 43 and 68% in Nevada, and 11 and 13% in California (all in 2006 and 2007, respectively), and 3.3% in Kansas and 2.7% in Missouri (both only in 2007). Elevated abundances of S. schevyrewi at survey sites in Colorado and Wyoming could be the result of competitive displacement of S. multistriatus by S. schevyrewi, whose occurrence and mechanism require further study. General seasonal trends from all sites indicated peak flight in July and August for S. schevyrewi and two peaks (May-June and July-August) for S. multistriatus. Funnel traps baited with Multilure and 2-methyl-3-buten-2-ol were highly attractive to S. multistriatus, and mildly attractive to S. schevyrewi, whereas panel traps caught few beetles. The U. pumila trap logs were a more sensitive monitoring tool for detecting the presence of S. schevyrewi.