Pecan carpenterworm
Cossula magnifica (Strecker)
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. Pecan, hickory, oak. Pecan and hickory are the
major hosts (Matz 1918, Moznette and others 1931, USDA FS 1985). Does not
attack oaks to the same extent as pecan and hickory, but among oaks, favors
white oak. Post oak, scarlet oak, and black oak also recorded as hosts.
Range. Distributed from North Carolina and Florida west to Texas
and Mexico and Guatemala (Matz 1918, Moznette and others 1931, USDA FS 1985).
Description
Adult. Grayish moth mottled with brown and black blotches (Gill
1924, Moznette and others 1931, USDA FS 1985). Forewings mottled with
small brown patches, and each has large brownish area at distal end; hindwings
uniformly darker without distinct markings. Wingspan ranges from 37 to 44
mm.
Larva. Pinkish and naked or only sparsely covered with short,
fine setae that arise from numerous tubercles. Head, cervical shield, and
anal plate shiny dark brown. Mature larvae may reach 37 mm in length.
Pupa. Brown and has sharp projections on head, used to help
force its way through pupal cell and along larval burrow to exit hole.
Biology. Adult moths emerge late April through June and deposit
eggs on the bark of small branches in the tops of trees (Gill 1924, Moznette and
others 1931, USDA FS 1985). Newly hatched larvae first attack small twigs
and branches, tunneling out the pithy centers. When too large for the
small twig, larvae crawl out and enter a large branch. Entrances in
twigs and small branches usually adjacent to buds, leaf petioles, or small
secondary branches. Larvae may tunnel up to 10 cm in both directions from
the entrance holes, leaving only shells of small branches 9 to 13 mm in diameter
(Solomon and Payne 1986). By early fall, larvae vacate branch galleries,
move downward, and bore into the trunk and large branches. Larvae
attacking the trunk usually initiate galleries in bark crevices and tunnel
horizontally or obliquely upward 13 to 32 mm, then vertically for another 6 to
13 cm. Many larvae also tunnel downward from the points of entrance
another 5 to 10 cm. Cross sections of the vertical portions of the
galleries are usually round and 6.5 mm in diameter. Larvae overwinter in
their galleries. In April or May, mature larvae enlarge the entrance
holes, then enclose themselves in the upper ends of the galleries behind
networks of threadlike material. Just before emergence, the pupae, using
sharp projections on the heads, move through the barriers and down the tunnels
to the entrance holes. The life history is little known, but the species
appears to have one generation per year.
Injury and Damage. Entrance holes may be obvious on the trunk
but the earliest signs of attack are sapstained bark and small quantities of
moist frass at entrance holes on small branches (Solomon and Payne 1986).
Splitting an infested branch reveals the gallery. Signs are often
overlooked because infested branches may be high above ground and the frass
scatters as it falls. Attack sites become easier to recognize when larvae
later bore into the trunk during fall (Moznette and others 1931, Turner and
others 1918). Most attack sites are concentrated around the base of the
trunk from groundline up to about 1.2 m. Attack sites in the trunk are
characterized by small circular entrance holes about 6.5 mm in diameter, with
sapstained bark below the entrances and a few excrement pellets and fine frass
in bark crevices. Galleries may extend both upward and downward from the
points of entrance. Pelletlike frass often accumulates in piles on the
ground around the bases of infested trees. Entrance holes are enlarged to
about 9.5 mm just before pupation. Brown pupal skins may be found
protruding from entrance holes after moths emerge during May and June.
Vacated galleries heal over, leaving uniformly round or oval bark scars for
several years as evidence of attack. Branches and trunks of trees of all
sizes are attacked, but those 8 to 31 cm in diameter are preferred. Small
branches may break or die back at tunneled sites. Although very few trees
break or die, heavy repeated attacks may structurally weaken a tree, reduce its
vigor, and provide entry for decay fungi and other pathogens. Wormholes
degrade and markedly reduce the value of sawlogs and lumber. Populations
may be heavy locally, but widely scattered infestations and sporadic appearances
minimize overall economic impact.
Control. Although largest populations occur in South, damaging
infestations are widely scattered and quite localized (Boethel and others
1980). Trees planted in orchards, groves, as ornamentals, or other-wise
open grown are generally more heavily infested than those in well-stocked forest
stands. New plantings should not be established adjacent to heavily
infested old orchards. Infestations can be minimized by keeping trees
vigorous and free of disease cankers and mechanical injuries. Two tachinid
parasites--Phorocera comstocki Williston (Leiby 1925) and P. signata Aldrich
and Webber--have been reared, but little is known of their effect on
populations. Insecticides used regularly in managed groves to control nut
and foliar insects provide some, but not complete, control. Chemical
control specifically for pecan carpenterworm is seldom used (Boethel and others
1980).
Adult(s) male. James Solomon,
USDA Forest Service. |
Larva(e) in gallery. James Solomon,
USDA Forest Service. |
Damage entrance hole in branch. James Solomon,
USDA Forest Service. |
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