Little carpenterworm
Prionoxystus macmurtrei (Guerin)
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. Red oaks, chestnut. Northern red oak principal oak
host (Hutchings 1924a, 1924b); also reported from black oak (Tietz 1945).
Probably attacks other species in red oak and white oak groups.
Range. Mainly eastern Canada and the northeastern United States,
as far south as Texas and as far west as Minnesota (Hutchings 1924a).
Description
Adult. Gray-black moth; female with spindle-shaped body covered
with dark gray scales; forewings mottled with gray and black, hindwings mostly
clear (Hutchings 1924b). Males with dark gray bodies with wings mostly
clear and shining except for scattered gray-black scales. Wingspan about
60 mm in female and 35 mm in male. Males bear little resemblance to
females in color and size and are easily mistaken for another species.
Egg. Oval shaped, measuring about 3 mm by 1.5 mm. When
first laid, dull greenish yellow, turning dull brown (Hutchings 1924a).
Larva. Newly hatched about 5 mm long. When fully grown,
female larvae are about 63 mm long and 15 mm wide; males about 38 mm long and
less robust than females. Head and thorax of larvae dark brown. Body
changes during development from pinkish white to bright pink by end of first
season, to dull greenish white in full-grown larvae (Hutchings 1924b).
Dark tubercles that appear on body during first season lass distinct in fully
grown larvae (Hutchings 1924b).
Pupa. Rounded, shiny, and reddish brown to mahogany.
Female pupae about 46 by 11 mm; males about 25 by 6 mm (Hutchungs 1924b).
Biology. Moths emerge mostly from late May through early
July. Males are strong fliers and strongly attracted to females.
Mating occurs shortly after emergence, and oviposition soon begins. Eggs
are laid singly or in small groups, usually in bark crevices or other rough
areas of bark. Females can lay 50 to more than 275 eggs in about a
week. Female moths die soon after oviposition. Eggs hatch in 10 to
13 days (Hutchings 1924a). Young larvae usually excavate burrows in and
under bark near egg sites. Cavities are expanded during summer and measure
about 25 mm in diameter and 9 to 13 mm deep at first season's end. Larvae
spend their first winter in the excavated burrows and resume feeding in spring,
extending their tunnels deeper and wider in the inner bark and outer layers of
wood. When two or more larvae feed close to one another, an area several
centimeters across may be skeletonized. During the second summer, larvae
move inward, tunneling the outer layers of sapwood initially and then
heartwood. After overwintering in heartwood, the larvae feed inward and
usually upward. By the end of the third summer, tunnels are uniform in
diameter with enlarged bark exits. During the last fall, mature larvae lay
down soft, silklike coverings on the gallery walls. Pupation occurs behind
silken, feltlike curtains within the galleries the next spring. Just
before moth emergence, pupae move down the galleries and partially through the
exit openings. Moth emerge and crawl upward onto the bark.
Injury and Damage. New larval activity can be detected by small
quantities of fine, brown, sandlike borings held loosely together by invisible
silken threads in crevices of the bark and around the crevices of scars.
Bark discolored by oozing sap may also indicate new attacks. Older larvae
eject frass of wood chips and excrement pellets from large openings in trunks
and branches (Solomon 1977b). Galleries extend for a short distance under
bark and then generally extend inward and upward. There may be
considerable crossing and intersecting of galleries. Gallery size varies
greatly but ranges from 8 to 12 mm in diameter and 15 to 30 cm long.
Unsightly bulging scar tissue usually forms around exterior openings. All
parts of a tree over 3 cm in diameter are susceptible to attack, and branches
that have been girdled or small branches that have been tunneled may break and
die. A tree that is repeatedly attacked becomes badly honeycombed, and its
interior may be converted into a labyrinth of dark tunnels that cross and
intersect form many directions (Hutchings 1924a). Such damage markedly
reduces its value for lumber (Donley 1974). Trunk wounds healing from the
outside from thick, horny, bulging scars that reduce the beauty of
ornamentals. Branches may be tunneled, resulting in breakage, or girdled,
causing dieback. Trees with such top damage may become asymmetrical.
Damage is similar to that caused by P. robiniae (Peck), but total impact
is much less because of localized, scattered populations and limited
distribution.
Control. Woodpeckers and other birds are the most important
natural enemies. Young larvae burrowing in the bark are especially
vulnerable (Hutchings 1924a). Nuthatches, brown creepers, and chickadees,
warblers, and other birds feed on the eggs and newly hatched larvae. An
unidentified dipterous parasite has been reared from a 2-year-old caterpillar
(Hutchings 1924a). Brood-tree removal will help to reduce damage.
Insecticides or fumigants can effectively prevent and control small
carpenterworms in high-value trees.
Adult(s). James Solomon,
USDA Forest Service. |
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