Boxelder twig borer
Proteoteras willingana (Kearfott)
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. Boxelder, maple. Boxelder is the major, possibly
only, host (Peterson 1958). However, other maples have been mentioned as
hosts (MacAloney and Ewan 1964).
Range. Throughout the eastern United States west through the
Great Plains. Also found in southern Canada. Most troublesome in the
Great Plains of the United States and the Prairie Provinces of Canada, where
boxelder is grown extensively for shade and farm shelterbelts (Peterson 1958).
Description
Adult. Small, gray-mottled moth with wingspan of 15 to 25 mm;
female slightly larger than male (Anonymous 1971, Peterson 1958). Wings
with white to pale brown fuscous ground color overlaid with streaks, rings, and
clusters of yellowish tan to black scales. Males with black subcostal
streak on each forewing and black costal streaks on hindwing. Both sexes
with four clusters of raised scales on each forewing.
Egg. Round to elliptical, depending on closeness to leaf vein or
midrib, with flangelike margins. Translucent, pearly white, and from 0.46
to 0.58 mm long and 0.33 to 0.50 mm wide (Peterson 1958).
Larva. Yellowish white with light brown head and eye spots,
later changing to greenish yellow with dark brown head (Peterson
1958). Older larvae whitish yellow with brown to black heads with oval,
grayish black, raised cuticular areas bearing setae above and below abdominal
spiracles. Mature larvae measure 6 to 13 mm long (Anonymous 1971, MacKay
1959).
Pupa. Reddish brown and from 7 to 11 mm long (Peterson 1958).
Biology. In Canada, adults are present from late June to late
July, flying with a darting motion. They are most active in evening,
frequently resting on trunks or ground but seldom on leaves. Moths live 15
to 20 days at most. Females begin laying eggs soon after becoming adults
and may deposit 100 or more eggs, mostly during the evening. Eggs are
deposited singly on the undersides of leaves, usually close to the midribs or
large veins. The egg stage lasts 9 to 14 days, with a mean of 11 days
(Peterson 1958). Eggs hatch from early July to early August (Anonymous
1971). Newly hatched larvae begin feeding along the veins or midribs,
usually on the lower leaf surfaces. They construct rooflike shelters of
webbing and frass over themselves and feed on the protected leaf surfaces.
The first two instars, about 11 to 23 days, are spent in shelters on the
leaves. Third-instar larvae move to the base of petioles and bore into
dormant leaf buds. Most larvae terminate this period in about 22 days by
molting to the fourth instar, usually in late September, October, or
November. The winter is passed in the fourth instar in silken cocoons
within the dormant leaf buds. In Canada, during late April to late May,
larvae vacate their winter quarters and burrow into other buds, where they feed
actively. Each larva may destroy two or three buds during this
stage. In May or June, larvae molt to the fifth instar, abandon the buds,
and bore into the new stem growth of twigs and terminals. Larvae feed
within the swollen or galled shoots until fully grown in May or June.
Then, they drop to the ground and prepare pupation cells of silk and leafduff in
the humus layer of the soil. The pupal period ranges from 13 to 18 days
and averages 16 days (Anonymous 1971). The earliest recorded emergence of
adults is June 19; the latest is July 23 (Miller 1987, Peterson 1958). The
life cycle is 1 year.
Injury and Damage. Two kinds of injury are important. The
first, observed mostly in Canada, is the destruction of dormant buds from
mid-August to early fall and from late April to early May (Anonymous
1971). The second, larval burrowing in succulent growing shoots, causes
stem breakage stunting, and mortality. Fine, dark brown or black frass
often protrudes from entrances a few centimeters below the apex or from the
shoot tip. Feeding activity stimulates infested twigs to enlarge
abnormally, forming spindle-shaped, gall-like swellings. Larval entrance
holes can be found usually toward the lower ends of the galls. Burrows
become quite extensive, resulting in tunnels 25 mm or longer. Splitting
the swollen shoots reveals tunneling larvae. It attacks trees of any age,
from first-year seedlings in nurseries to mature trees in urban and rural
plantings. This borer occurs in almost all boxelder plantations in
Manitoba, Saskatchewan, and Alberta. Up to 50% of the new growth may
become infested with up to 30 twigs infested on a stem. New shoots are
often killed or break, and terminal growth is prevented. Heavy outbreaks
stunt established trees by killing much of the current tip growth on twigs and
branches. Secondary branching results, and when this growth is also
destroyed, the affected trees may fork repeatedly, becoming bushy and
undesirable as shade trees (MacAloney and Ewan 1964).
Control. Parasites and diseases are beneficial in controlling
the borer. Sometimes up to 30% of the larvae are parasitized (Anonymous
1971, Peterson 1958). Insect parasites recorded include Ascogaster sp.,
Atrometus clavipes (Davis), Bassus sp., Campoplex crassatus
(Viereck), Cremastus similis (Cushman), Elachertus (hyssopus) sp.,
Erynnia torticus (Colquillett), Euderus cushmani (Crawford), Lissonota
sp., Macrocentrus delicatus Cresson, and Pristomerus euryptychiae
Ashmead (Arnaud 1978, Burks 1979, Carlson 1979, Marsh 1979, Peterson
1958). Campoplex crassatus is by far the most important
parasite. Direct control practices can help to minimize injuries in shade
and ornamental trees. Removing and burning secondary sucker growth and
galled twigs in late fall or early spring are recommended. Treating
foliage during mid-July to early August with recommended insecticides provides
effective control (Drouin and Kusch 1979).
Damage twig swelling with frass at entrance hole. James Solomon,
USDA Forest Service. |
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