Carpenterworm
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Hosts
Oak, elm, willow, poplar, ash, boxelder, black locust, sugarberry, sycamore. First recorded as "riddling black locust" in Massachusetts (Peck 1818). Wide range of hosts, but certain species are preferred, depending on location and availability (Hay and Morris 1970). In the East and South, oaks are preferred (particularly those in red oak groups); in southern bottomlands, overcup oak (white oak groups). In the prairie region, chief hosts are green ash and elm; in the Rocky Mountains, poplars; and in California, coast live oak and introduced elms. Occasionally attacks fruit trees, ornamental shrubs, and other hosts.
Range
A native of North America, widely distributed throughout the United States and southern Canada (Solomon and Hay 1974).
Description
Adult
Large, grayish, stout-bodies moth, with uniform mottling of gray and black scales over body and wings. Moth protected by its coloration; at rest on bark of oak, its gray and black mottling harmonizes closely with bark color, making it almost invisible. Female twice size of male; average wing-spread of females 75 mm. Posterior half of each of male's hindwings covered by yellowish orange spot.
Egg
Dark olive brown, oval 2.3 mm long by 1.5 mm wide.
Larva
Newly hatched 6 mm long and reddish pink with dark head. As larva matures, gradually becomes greenish white. Mature larvae 50 to 75 mm long; shiny dark brown heads with powerful black mandibles.
Pupa
Dark, shiny brown, 37 to 50 mm long, broad at head end, tapering to blunt point at hind end, with pair of toothed bands on dorsal surface of abdominal segments.
Biology
Moths emerge in late April to early July, varying by region from south to north. Females produce sex attractant that lures males form long distances. Mating occurs in the afternoon and ceases by nightfall. During the night, females deposit 200 to 1,000 eggs singly or in small groups in bark crevices and under vines and lichens. Eggs hatch in 10 to 13 days. Newly hatched larvae construct loose silken webs and bark coverings and either begin their boring or move elsewhere to make their entry. Young larvae feed initially in the phloem and cambium but soon initiate crooked galleries into the sapwood. As larvae approach maturity, they chew away the sides of the crooked galleries to facilitate exit of pupae. Larvae keep galleries open or only loosely plugged with frass. During spring of the last year of development, full-grown larvae partially line the tunnel with yellowish brown silken threads before pupating in the innermost part of the galleries. Three to six weeks later, pupae wriggle to the exits where the moths emerge. Empty pupal cases remain in place unless dislodged. Many female moths are so heavily laden with eggs that they cannot fly until they have deposited many of their eggs on the same tree from which they emerged. The life cycle is 1 to 2 years in the South and 2 to 4 years in the North.
Injury and Damage
Earliest signs of attack are sap spots with fine frass mixed with sap ooze. Later, stained bark spots become larger, and frass (wood chips and excrement pellets) is ejected from entrance holes. Frass often becomes profuse at the entrances, in bark crevices, and around the bases of infested trees. Usually, larvae hollow out irregular, cavelike burrows 50 mm in diameter under the bark. Galleries 12 to 16 mm in diameter and 12 to 22 cm long extend obliquely upward, then straight upward in the sapwood and heartwood. Wounds usually heal in 1 to 2 years, leaving oval to irregular bark scars that remain as evidence of attack for 10 to 20 years. Empty pupal cases protrude from the bark until dislodged. Damage in sawn lumber appears as pockets of ingrown bark and oval or irregular holes 12 mm or larger in diameter surrounded by stained wood. Stain may extend from a few centimeters to 60 cm up and down the trunk from the gallery. The inner surface of the hole is dark stained. Until recent years, this borer mainly attracted attention as a pest of shade and ornamental trees (Doten 1900, Felt 1905) and windbreak trees (Munro and Fox 1934). Foresters are now taking notice on its effect on hardwood timber in forest stands. Degrade from its damage has been estimated at 15% of the value of roughsawn oak lumber (Hay and Morris 1970). It is a major contributor to the $20.65 per thousand board foot average loss in oaks attributed to insect borers in the South (Morris 1977). Infested trees are seldom killed, but young trees honeycombed by several generations of borers may be broken off by wind.
Control
Natural enemies suppress the carpenterworm but often do not keep damage to acceptable levels. Two hymenopterous parasites--Lissonota prionoxysti (Rohwer) and Pterocormus devinctor (Say)--have been found (Carlson 1979); the first reportedly reduced moth emergence by 12% in an eastern Kentucky population (Hay and Morris 1970). The entomogenous nematode Steinernema feltiae Filipjev has shown some promise for control (Lindegren and Barnett 1982). Disease organisms--especially Beauveria bassiana (Bals.) Vuill.--have been found, but natural infection is low. Predators, including spiders, insects, and birds, are the most important natural enemies. Spiders are particularly important predators of newly hatched larvae. A small carabid, Coptodera aerata Dej., consumes many first- and second-instar larvae. Birds, especially woodpeckers, are also important predators. Woodpeckers have been credited with capturing upwards of 75% of young carpenterworm larvae in North Dakota (Munro and Fox 1934). The hairy woodpecker effectively excavates carpenterworm larvae from galleries in small trees under 15 cm in diameter. Other birds observed capturing moths include the Arkansas kingbird, common kingbird, red-bellied woodpecker, redheaded woodpecker, Carolina wren, summer tanager, and blue jay. Cultural practices that promote tree vigor, prevent bark injuries, and remove brood trees help to minimize damage. Treating galleries with commercially available fumigants and insecticides is effective for individual high-value trees (Solomon 1985a). Trunk-applied insecticides times with the use of sex attractants to correspond with egg hatch are effective in preventing infestation.
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. Argic. Handbk. 706. Washington, DC: U.S. Department of Agriculture, Forest Service. 735 p.
