Poplar branch borer
Oberea schaumii LeConte
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. Poplar. Quaking aspen, bigtooth aspen, Lombardy
poplar, Carolina poplar, eastern cottonwood, and plains cottonwood have been
listed (Nord and others 1972a) Eastern cottonwood is preferred in the
South, and quaking aspen has been mentioned most often in the North.
Range. Southern Canada and southward throughout much of the
United States south to Mississippi (Morris and others 1975).
Description
Adult. Slender, elongate longhorn beetle ranging in length from
12 to 16 mm. Coloration quite variable, ranging from mostly black to
brownish yellow or yellowish orange, causing some authors to describe color
forms and even subspecies (Allan and Knight 1976, Breuning 1960, Nord and others
1972a). Males mostly black; females generally lighter.
Egg. Yellowish white, elongate, occasionally flattened on one
end and about 2.5 mm long.
Larva. Legless, narrow, very slender, yellowish white except for
dark mandibles develops to 12 to 25 mm long.
Pupa. Yellowish white (Morris and others 1975).
Biology. Adults emerge April to June and are sometimes present
until early August (Morris and others 1975, Nord and others 1972a). After
a few days of feeding and mating, females begin laying eggs in niches gnawed in
the bark (Grimble and others 1969). They select stems for ovipositing
sites that are mostly 5 to 15 mm in diameter and 1 to 6 years old (Nord and
others 1972a) but may be up to 38 mm in diameter (Morris and others 1975).
Usually eggs are deposited singly between the wood and bark below the egg niches
and hatch in about 2 weeks. Young larvae bore toward the center of the
stem and then downward, ejecting frass the first summer through a split in the
bark along one side of the egg niches and in subsequent years through circular
holes cut to the outside from the central tunnel. The life cycle may be 1
to 2 years in the South (Cook and Solomon 1976) to 2 to 4 years in the North (Nord
and others 1972a). Thus, the length of the central tunnel and the number
of ejection ports will also vary, as activity is greater when the life cycle is
longer. Near the end of the larval stage, larvae tunnel upward above their
egg niches and outward to just under the outer layers of bark. Fully
developed larva pack the lower end of the tunnels with granular frass and
fashion loose plugs of long, fibrous frass in the upper part of their
tunnels. Pupation occurs behind frass plugs in the upper portion of the
tunnels. New adults chew through the bark covering the tunnels to
exit. There is a positive relation between this borer and canker
fungi. At least a third of the cankers in quaking aspen have occurred at
borer-infested sites (Nord and Knight 1972).
Injury and Damage. Egg niches gnawed in the bark are early signs
of infestation. Egg niches are elongate, rectangular, and 5 to 11 mm long,
about 3 mm wide, and usually parallel to the stem axis. Feeding by newly
hatched larvae begin beneath the cambium tissue and is evidenced by fine frass
in and around splits in the bark at the site of the egg niche. After a few
weeks of stem growth, the egg niches become more prominent, appearing as two
parallel splits in the bark. After the young larvae bore into the stem, they
tunnel downward parallel to the stem axis. During the first summer, the
larvae make tunnels about 25 mm long. In subsequent years, they lengthen
and widen the tunnels so that the final dimensions may be as much as 16cm by 4
mm. Although a moderate amount of frass is packed within the gallery, they
eject some through the oviposition slit during the first year and some through
secondary and tertiary ports made along the stem. During development, some
of the external openings may become closed by callus or scar tissue (Nord and
others 1972a). Callus growth sometimes causes the affected area to appear
swollen. Emerging adults leave round, 4-mm diameter exit holes in the
branches. When adults emerge, they conspicuously feed on the midribs and
branch veins of the leaves (Morris and others 1975). Terminal breakage may
result in crooked trunks, forking, and heavy branching in individual trees (Cook
and Solomon 1976). Breakage, however, is uncommon except when multiple
infestation occurs within the stem. Economic loss in stands of large trees
and in well-stocked sucker stands is usually light to negligible (Nord and
others 1972a). Infestations in aspen sucker stands in Michigan have ranged
to 17% without serious impact. However, infestations appear to be greater
in planted or open-grown trees. Therefore, impact is apt to be greatest in
young monoculture plantings under intensive management.
Control. Natural controls are very important, destroying up to
98% if some populations (Grimble and Knight 1971). Egg non-viability has
been estimated at 21%. Dessication of young larvae accounts for some
mortality. Five hymenopterous parasites--including Cenocoelius
sanquineiventris (Ashmead), Cremastus nordi Townes, Dolichomitus
messor perlongus (Cresson), Iphiaula eurygaster (Brulle), and Xylophrurus
bicolor (Cushman)--and three dipterous parasites--Lixophaga n. sp., Megaselia
n. sp. and Odinia sp. near xanthocera Collin--have been
reared. Parasitism rates have ranged up to 63% for some collections.
Predation by woodpeckers has ranged form 5 to 25% in Michigan and up to 40% in
Mississippi. Unidentified diseases are also important natural
controls. In Mississippi, woodpeckers predation and disease appear to be
the major natural controls (Cook and Solomon 1976).
Adult(s). James Solomon,
USDA Forest Service. |
Damage stem. James Solomon,
USDA Forest Service. |
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