Hickory Agrilus
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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.
Gallery
 Photo by James Solomon, USDA Forest Service, Bugwood.org |  Photo by James Solomon, USDA Forest Service, Bugwood.org |
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.
