Hickory agrilus
Agrilus otiosus 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. Hickory, pecan. Water hickory and pecan are
commonly infested, but other hickory species undoubtedly are infested (Fisher
1928, Wellso and others 1976). Persimmon, dogwood, maple, redbud, black
walnut, butternut, hazel, oak, and black locust mentioned as hosts in the early
literature (Chittenden 1900b, Leonard 1928, Mutchler and Weiss 1922), but these
observers probably mistook other Argilus species for A. otiosus
(Fisher 1928).
Range.An eastern species commonly reported from Massachusetts
and New York west to Minnesota and Kansas and south to Georgia and Mississippi
(Fisher 1928, Franklin and Lund 1956).
Description
Adult. Small, slender, nearly linear, and moderately shining
beetle 4 to 5.8 mm long and about 1.3 mm wide (Fisher 1928, Knull 1925).
Head and antennae greenish blue, pronotum dark bronzy green with sides more
bluish, and elytra black with strong greenish or bronze tinge. Beneath,
beetles dark bronzy green and more shining than above. Pronotum slightly
wider than long and elytra slightly wider than pronotum.
Biology. Adults begin emerging in May and June throughout the
range of the species and have been collected as late as August in its northern
distribution (Fisher 1928, Leonard 1928). Larvae hatch from eggs laid on
the bark and burrow into the phloem. Larval burrows generally are in the
inner phloem-cambium, but sometimes portions of burrows occur entirely in the
phloem. The larvae tunnel downward in spirals or zigzags for long
distances, making galleries that measure up to 1.8 m long. In trunks 6 to
16 cm in diameter, early tunneling is characterized by a spiral pattern, but
older larvae more commonly make zigzags. Larvae may circle small stems as
many as six times in their travel down the trunk. The insect's life
history is little known, but based on gallery lengths and characteristics, the
life cycle appears to be more than 1 year.
Injury and Damage. Active infestations are difficult to
detect. After the borers complete development and exit, spiral and zigzag
swellings appear in the bark on trunks of young trees. Removing the bark
from the swollen areas reveals larval burrows. Years later, multiple
spiral and zigzag grooves are prominent on the bark of large trees. Bolts
taken from infested trees and sliced, split, or sawn open will reveal the small,
oval (in cross section), frass-filled larval burrows in the phloem. In
sawn lumber, small, dark brown spots, sometimes with bits of frass and ingrown
bark, appear as defects similar to bird pecks. Small D-shaped exit holes
can sometimes be found in the bark of young trees. This stem-boring beetle
produces minor defects in the wood but does not cause mortality. In the
Deep South, water hickory on wet sites in the bottomlands of Arkansas,
Louisiana, and Mississippi seems particularly susceptible, and young pecan
plantings have been heavily infested.
Control. One hymenopterous parasite--Bephratoides agrili
(Ashmead)--has been reported, but nothing is known of its effectiveness (Burks
1979). Open-grown planted trees appear most susceptible.
Damage sinuate gallery under bark. James Solomon,
USDA Forest Service. |
Damage zig-zag grooves in outer bark. James Solomon,
USDA Forest Service. |
Damage note spiral swellings in bark over gallery. James Solomon,
USDA Forest Service. |
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