(Kearfott)
Solomon, J.D. 1995. Guide to Insect Borers in North American Broadleaf Trees and Shrubs. Agriculture Handbook 706. Washington, DC. United States Department of Agriculture, Forest Service. 735 p.
Contents
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).
