Survey of Shoot Damage Caused by the Exotic Pine Shoot Beetle in Michigan Pine Stands

The exotic pine shoot beetle, Tomicus piniperda [L.] (Coleoptera: Scolytidae) is a Eurasian pest of pines that was first discovered in North America in 1992 near Cleveland, Ohio. It has since been found in at least 72 counties in Michigan, 285 additional counties in 11 other north central and eastern states, and the provinces of Ontario and Quebec. We counted injured shoots along linear transects in ten stands of Scotch (Pinus sylvestris L.), red (Pinus resinosa Aiton), and jack pine (Pinus banksiana Lambert) in lower Michigan (30 stands total) to estimate the frequency of shoot damage attributable to pine shoot beetle, other shoot-feeding insects, weather, and other damaging agents from 1997 to 1999. Fifteen of the stands were located in southwestern counties where pine shoot beetle has been established for at least 8 to 10 yr. The other 15 stands were in northern counties where pine shoot beetle establishment is more recent. In the southwestern stands, pine shoot beetle killed significantly more shoots in Scotch pine stands than in red or jack pine stands, and injured more shoots in Scotch pine stands than all other insects combined. Two of these Scotch pine stands were near an area with an abundance of Scotch pine brood material available to parent beetles. Damage in these two stands averaged roughly 10 to 12 shoots per m2 in 1998 and 1999, compared with 0.6 to 1.6 shoots per m2 in other Scotch pine stands, and less than 0.2 shoots per m2 in nearby red or jack pine stands. Pine shoot beetle was at very low or undetectable levels in northern stands in all years. Shoots injured by three other shoot-feeding insects were occasionally encountered, most often in red pine stands, but caused an insignificant amount of damage. With the exception of the southwestern Scotch pine stands, most of the shoot damage, particularly in northern jack pine stands, was attributable to squirrels or abiotic factors such as wind, ice or snow. North. J. Appl. For. 18(4):101–109.