Poplar twig borer
Oberea delongi Knull
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. Eastern cottonwood is preferred (Hicks
1962, Morris and others 1975). The insect has been observed less
frequently in swamp cottonwood and occasionally in hybrid poplars. It
probably occurs in other poplar species.
Range. Eastern United States from Michigan to Massachusetts
south to the Gulf Coast and west to Kansas, from Ontario and Quebec in
southeastern Canada (Hicks 1962, Morris and others 1975).
Description
Adult. Slender, elongate longhorn beetle measures 10 to 14 mm
long and 2.5 mm wide (Knull 1946). Antennae of male extend to apical
fourth of elytra; female antennae slightly shorter. Coloration of head,
prothorax, and ventral surfaces somewhat variable, ranging from yellow to black;
legs yellow; and elytra usually black with outer margins yellow. Surfaces
of elytra faintly ridged, with coarse punctures between ridges.
Egg. Creamy white, cylindrical, about 3 mm long and 0.5 mm in
diameter.
Larva. Greatly elongate, slender; and nearly cylindrical except
body segments, which gradually decrease in width toward rear. Body smooth,
shiny, and pale yellow except for brown head, dark brown mandibles, and light
brown thoracic shield. Mature larvae about 19 mm long.
Pupa. White and delicate and 8 to 12 mm long.
Biology. Adults emerge from April to June in the Deep South
(Cook and Solomon 1976) and from mid-June through July in Michigan (Gosling and
Gosling 1977). Adults feed extensively on the leaf midribs and large
lateral veins after they emerge and mate. Females deposit eggs singly in
niches chewed in the bark with their mandibles, typically selecting green shoots
5 to 13 mm in diameter. The niches remain visible for weeks after
oviposition has ended. Eggs hatch in about 2 weeks, and larvae tunnel down
the center of the stem, expelling little or no frass from the entrance
holes. Larvae continue to feed into fall and overwinter in the shoots;
feed briefly the following spring, and pupate within shoot galleries in
March. Completed galleries range from 63 to 76 mm long and 3 to 5 mm in
diameter. This twig borer completes a life cycle in 1 year (Cook and
Solomon 1976, Morris and others 1975).
Injury and Damage. The beetles injure foliage by feeding on the
leaf midribs and, primarily, lateral veins, indicating that females are
ovipositing in nearby twigs (Morris and others 1975). Egg niches are most
common on twigs 6 to 10 mm in diameter, but larvae may be found in stems up to
13 mm in diameter. Infested branches usually become enlarged and appear
swollen or even gall-like and frequently become slightly crooked at the point of
attack. Larvae of this borer do not make a series of holes at regular
intervals through which to eject frass as do many other species of Oberea.
Infested twigs and terminals may be stunted or die back and occasionally break,
especially when worked by woodpeckers. Dissection of infested twigs
reveals dark galleries, partially filled with frass and the yellowish, elongate
larvae. Round, exit holes about 2.5 mm in diameter are left in the swollen
portion of the stem, or slightly below, by the emerging beetles. Damage is
most destructive when terminals are attacked, often producing crooked, deformed,
or excessively branched trees. Infestations have been observed in
nurseries, plantations, natural stands, and ornamentals, but damage has been
greatest in young plantations, adversely affecting tree form in crop
trees. Damage has been greatest in the lower Mississippi River Valley
(Cook and Solomon 1976).
Control. Woodpeckers, especially the downy woodpecker, are among
the most important natural controls (Cook and Solomon 1976). Local counts
have estimated predation rates up to 60% during some years. Unidentified
diseases kill sizeable numbers of larvae, especially during wet springs.
Direct controls have rarely been needed.
Adult(s) feeding on leaf (note veinal feeding). James Solomon,
USDA Forest Service. |
Damage stem. Lawrence Abrahamson,
State University of New York. |
Larva(e) and stem damage. James Solomon,
USDA Forest Service. |
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