Granulate Poplar Borer
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Hosts
Poplar. Reared from Lombardy poplar, eastern cottonwood, and black cottonwood (Fisher 1928, Mutchler and Weiss 1922).
Range
The Great Plains eastward to New York, south to North Carolina and Louisiana, and west to Colorado and Montana (Carlson and Knight 1969, Fisher 1928). In Canada common in both native and planted poplars, particularly in the grassland and southern regions of Alberta (Brown and Stevenson 1965).
Description
Adult
Slightly flattened, olive brown beetle, moderately shining, narrow, and 7 to 11 mm long (Fisher 1928). Males slightly shorter and more slender than females. Body covered with short, recumbent, whitish pubescence. Each elytron ornameted with three spots of more dense whitish to golden hairs, one in basal depression, one in front of middle, and other near apical fourth. In living beetles, these spots distinguish this species from A. g. litragus Barter and Brown (Carlson and Knight 1969, Fisher 1928).
Larva
Elongate, very narrow, and 27 to 40 mm long. Body flattened with widened prothorax, white except for brown mouthparts and anal forceps.
Biology
Adults emerge during June and July (Mutchler and Weiss 1922, Packard 1890) and feed on the foliage of host trees. Females deposit eggs in crevices of rough bark on branches and trunks of susceptible trees. They prefer trees severely weakened by drought, disease, and poor site conditions (Ives and Wong 1988). In the beetle's southern range, populations are most prevalent in river bottoms at lower altitudes. Larvae usually feed and develop beneath the bark but occasionally tunnel into the wood briefly, then back to the cambium. In October, larvae bore obliquely into the wood 2.5 to 5 cm, a few centimeters up or down, then curving back to within 3 to 8 mm of the wood surface. Here, they enlarge the galleries and overwinter in a folded or bent position. Pupation begins in May and lasts about 2 weeks. The life history is little known, but it appears to have a 1- or 2-year generation similar to that of A. g. liragus.
Injury and Damage
Thin crowns and dying branches are early symptoms of attack. Trees from sapling to sawlog size may be attacked. Although sap spots occasionally appear on the bark, little other surface damage indicates early infestation. Extensive galleries can be exposed by removing bark. Galleries in the cambium vary from very tight zigzag loops extending vertically to those that meander without much pattern (Mutchler and Weiss 1922). Small D-shaped holes are left in the bark by emerging beetles. Infested trees may succumb suddenly or slowly over several years, depending on other stresses. The deaths of many trees previously attributed to drought are now charged to this borer (Brown and Stevenson 1965, Packard 1890).
Control
Woodpeckers have been observed feeding on the larvae, but their effectiveness has not been evaluated. Good cultural practices that promote high tree vigor and reduce the incidence of disease help to minimize infestations and losses.
References
Solomon, J.D. 1995. Guide to insect borers of North American broadleaf trees and shrubs. Agric. Handbk. 706. Washington, DC: U.S. Department of Agricultural, Forest Service. 735 p.
