Could the European Thanasimus formicarius Outcompete the North American Thanasimus dubius (Coleoptera: Cleridae) if Introduced to North America?

A federal quarantine was enacted in the United States (US) in the fall of 1992 in response to discovery of the Eurasian pine shoot beetle, Tomicus piniperda (L.) (Coleoptera: Scolytinae), in July 1992 in Ohio. The quarantine regulated movement of pine products (e.g., Christmas trees, nursery stock, and logs) at the county level from infested to uninfested US states. A classical biological program was considered for T. piniperda starting in 1995, focusing on the Eurasian clerid beetle Thanasimus formicarius (L.), an important predator of T. piniperda. Concerns were raised in 1996 that if T. formicarius were released in the US it possibly could outcompete the native clerid Thanasimus dubius (F.). We conducted a series of laboratory tests in 1996 to compare survival rates of T. formicarius and T. dubius larvae when added to bark beetle galleries on red pine (Pinus resinosa) bolts. Bolts were infested with one of three bark beetle species: Ips grandicollis (Eichhoff), I. pini (Say) or T. piniperda. The clerid species were added separately on some bolts or together on other bolts, sometimes at the same time or with T. formicarius preceding T. dubius by a week. For all treatments combined, 8.0% of T. dubius larvae survived to adults compared to 4.4% of T. formicarius. Survival of T. dubius was higher than T. formicarius on bolts infested with I. grandicollis and I. pini, but similar on bolts infested with T. piniperda. Overall, our results suggest that T. formicarius would not outcompete T. dubius if introduced. Although aware of our findings, USDA APHIS (United States Department of Agriculture, Animal and Plant Health Inspection Service) decided in 1997 not to release T. formicarius in the US.