Attack Densities of Tomicus pintiperda and Ips pini (Coleoptera: Scolytidae) on Scotch Pine Logs in Michigan in Relation to Felling Date

Abstract

Established populations of an exotic bark beetle, the larger pine shoot beetle [Tomicus piniperda (L.)], were first reported in Ohio in July 1992. Subsequent surveys through July 1994 have found T. piniperda in six states in the United States and in one Canadian Province in the Great Lakes region. One-meter-long trunk sections were cut from Scotch pine (Pinus sylvestris L.) trees felled from February through July 1993 in a forested site in southern Michigan, laid horizontally, allowed to undergo natural attack by bark beetles and associates, and later dissected. In southern Michigan in 1993, T. piniperda initiated spring flight in late March; the pine engraver [Ips pini (Say)], a native pine bark beetle, initiated spring flight about one month later in late April. Tomicus piniperda attacks (galleries) were found in logs cut during February through May. Attack densities of T. piniperda were highest in February-cut logs, and declined with subsequent felling dates. The highest T. piniperda attack density recorded for an entire log section was 263 attacks/m2 of bark area on one of the February-cut logs. Ips pini attack densities tended to increase with later felling dates. When I. pini attacked logs that had already been colonized by T. piniperda, I. pini galleries were mostly found on the upper log surface. When I. pini attacked logs with few or no T. piniperda, I. pini galleries were found on all log surfaces. By initiating spring flight several weeks before I. pini, T. piniperda is able to colonize much of the susceptible pine material and thereby may lower I. pini populations.