Dogwood twig borer
Oberea tripunctata (Swederus)
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. Dogwood, viburnum, elm, sourwood, blueberry,
rhododendron, azalea, laurel, poplar, willow, mulberry. Dogwood is
preferred, but elm is commonly attacked (Beal and others 1952, Dillon and Dillon
1972, Johnson and Lyon 1988). It occasionally infests fruit trees in the
genera Malus and Prunus as well as many shrubs.
Range. Distribution corresponds closely with that of flowering
dogwood in eastern and central North America; recorded from Maine south to
Florida and west to Texas, Kansas, and North Dakota (Craighead 1923, Johnson and
Lyon 1988).
Description
Adult. Elongate, slender longhorn beetle measuring about 14 mm
long and 2.4 mm wide (Knull 1946). Head black, but prothorax, greater part
of underside of body, and legs yellow. Pronotum with two smooth, black
dorsal bumps, and another black spot in front of scutellum. Pronotum
broader than long and cylindrical, with convex upper surface. Elytra
variable in color but generally yellowish tan with narrow, black line on inner
margins and broader black line on lateral
margins.
Egg. Yellowish, cylindrical, and slightly curved; measures 3 to
4 mm long and about 0.5 mm in diameter (Driggers 1929).
Larva. Mature larva pale yellow except for dark brown head;
measures 19 to 25 mm long with head capsule width of 1.2 mm (Craighead 1923,
Ruggles 1915). Larvae smooth, shiny, legless, and cylindrical; body
segments gradually decrease in width toward rear.
Pupa. Yellowish white, measuring about 13 mm long.
Biology. Adults emerge in April and May in north Georgia (Fattig
1947); common from May through July in Pennsylvania (Kirk and Knull 1926) and
from late May to early August in Michigan (Gosling and Gosling 1977). Peak
oviposition on blueberries in New Jersey is late June and early July;
oviposition apparently occurs at night (Driggers 1929). Before ovipositing,
females make two rings of punctures, 13 to 25 mm apart, and from 7 to 15 cm from
the tips of current shoots. They slit the bark between the girdling wounds
lengthwise and insert eggs singly under one of the bark flaps. Newly
hatched larvae bore into the stem between the two girdles, tunnel short
distances toward the twig tip, then reverse direction and bore down the center
of the stem. At regular intervals along the stem, larvae make small holes
to the bark surface through which they expel frass. Larvae overwinter
between two, fibrous frass plugs within the galleries. Galleries in elm
twigs measure up to 15 cm long (Ruggles 1915). Mature larvae girdle the
woody part of the stem, causing many stems to break. The larvae quickly
plug the girdled openings. Pupation begins in April and May and occurs in
small chambers behind fibrous frass plugs. The insect completes its life
cycle in 1 year in the South and over much of its range (Forbes 1911, Johnson
and Lyon 1988). However, it requires a 2-year life cycle in Minnesota (Ruggles
1915) and a 3-year one is implied on blueberries in New Jersey (Driggers 1929).
Injury and Damage. Wilting and dying of leaves on the tips of
terminals and twigs during summer are usually the first signs of infestation (Driggers
1929, Forbes 1911, Johnson and Lyon 1988). Adults also feed on the leaves,
making elongate elliptical holes along veins. As the season progresses,
larvae bore down the centers of twigs toward the main stem, making rows of small
holes at regular intervals in the bark along the twigs. Frass, in the form
of excrement pellets adhering in long chains, is ejected from the small
holes. Splitting the infested twigs reveals long narrow galleries in the
stem centers. Stems are partially to completely girdled at one or more
places by the larvae. Examining severed ends reveals characteristic
V-shaped cuts. Terminals of young trees may be killed back for distances
of several centimeters to 1 m. In seedlings, sprouts, and small shrublike
plants (such as sourwood, blueberry, rhododendron, azalea, and laurel) larvae,
in addition to killing the shoot tips, continue to burrow downward to the root
crown or below until the entire aboveground plant is killed. Injury by
this borer in the 1900's occasionally caused premature dropping of leaves and
twigs of street elms in Minneapolis to such an extent that it appeared as if an
early fall had arrived (Ruggles 1915). The insect has been very injurious
to red-osier dogwood in Chicago parks (Forbes 1911). Cultivated
blueberries in New Jersey are sometimes heavily damaged (Driggers 1929).
Injury is much more important to ornamentals than in forests.
Control. Two species of hymenopterous parasites--Bracon
cerambycidiphagus (Muesebeck) and Cremastus orbus
(Davis)--have been reared (Carlson 1979, Marsh 1979). Rates of parasitism
have varied from 50 to 80% (Driggers 1929, Ruggles 1915). Woodpeckers prey
on the larvae. In ornamental plantings, the infested twigs should be
pruned and destroyed before the adults begin emerging during spring.
Ornamentals and nurseries can be protected with insecticides applied to the
foliage and twigs during emergence and oviposition.
Damage infested branch flagging. James Solomon,
USDA Forest Service. |
Galleries. James Solomon,
USDA Forest Service. |
Damage series of holes on infested twig. James Solomon,
USDA Forest Service. |
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