Granulate poplar borer
Agrilus granulatus granulatus (Say)
From: 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.
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.
Galleries. James Solomon,
USDA Forest Service. |
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