Carpenterworm
Prionoxystus robiniae (Peck)
From: 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.
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.
Damage feeding laterally across trunk (note frass covering gallery). James Solomon,
USDA Forest Service. |
Larva(e) in gallery. James Solomon,
USDA Forest Service. |
Adult(s) female (figure 19B in USDA Forest Service Oak Pests book). James Solomon,
USDA Forest Service. |
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