Rednecked Cane Borer
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Hosts
Raspberry, blackberry, dewberry. Shows a decided preference for blackberry (Hutchings 1923) but attacks all varieties of raspberry and dewberry--wild and cultivated (Fisher 1928).
Range
Distributed from eastern Canada and New England westward to Minnesota and Kansas and southward to Texas, covering nearly the entire eastern half of the United States (Chittenden 1922, Fisher 1928).
Description
Adult
Narrowly elongated and cylindrical beetle (Chittended 1922, Slingerland and Crosby 1919). Elytra vary from beautiful velvety black to blue with bluish reflection. Thorax usually coppery red but sometimes golden, brassy, or blue. Readily distinguishable from other Agrilus spp. by its red pronotum (neck) from which it gets its name. Head small, dark, bronze, and deeply grooved. Antennae and legs very short relative to rest of body. Beetles 6 to 8 mm long and about a fourth as wide.
Egg
Irregularly oval and flattened, dirty white with brownish edges, from 1.0 to 1.5 mm across (Hutchings 1923).
Larva
Greatly elongated and flattened (Chittenden 1922, Lugger 1899, Slingerland and Crosby 1919). First thoracic segment prominent, being moderately flattened and widened at sides. Last segment of abdomen ends in pair of slender, forcep-like horns with three blunt teeth on inner edge of each. Larvae white to pale yellowish with brown head, measure 16 to 19 mm long (Chittenden 1922, Lugger 1899).
Biology
Around Washington, DC, adults appear as early as the first week in May. In more northern regions, they emerge from June until August (Chittenden 1922). Females oviposit from June to August on young cane growth, first near the root collar and later at points on the main stem and branches. Eggs are inserted in the bark near leaf bases and hatch in about 3 weeks (Hutchings 1923). The minute larvae feed beneath the bark and proceed spirally upward or downward in the wood parts causing the stems to swell and become gall-like (Chittenden 1922). They typically tunnel spirally around the cane two to six or more times, often girdling it (Slingerland and Crosby 1919). Later, larvae bore into the pith and continue upward or downward for 10 to 20 cm or more, sometimes causing stems to break. Mature larvae form oval pupal cells in the pith where they overwinter. Pupal cells typically are only a short distance above the ground and a few centimeters below the first gall. Pupation occurs during April and May and lasts 7 to 10 days. Adults exit through D-shaped emergence holes. This cane borer has one generation annually.
Injury and Damage
Larval tunneling causes irregular swellings or galls 2.5 to 10.2 cm long. Swellings initially are elongate or spindlelike but gradually enlarge and often exhibit multiple splits and become greatly roughened in appearance. The swellings sometimes form goutylike galls--hence, one of the earlier common names, the "gouty-gall beetle." Spiral burrows around the stem in these gall-like swellings are common, especially in raspberry canes; spindle-shaped swellings with splitting are more typical in blackberry and dewberry canes. Swellings and galls may occur at any point on the main stem and branches, but more commonly in the lower 0.3 to 0.9 m. Infested plants appear weakened and unthrifty, and fruits develop poorly. Cane breakage is common. The borer has been particularly destructive in cultivated plantings; heavy damage to blackberries in New Jersey has resulted in crop losses.
Control
Three species of insect parasites--Bracon sp., Microbracon xanthostigmus (Cresson), and Ptinobius magnificus (Ashmead)--have been reared (Chittenden 1922, Hopkins 1891). In one study, 18% of the larvae were destroyed by parasites (Hopkins 1891). Culturally, infested canes should be cut and burned during fall, winter, and early spring to destroy larvae (Chittended 1922, Lugger 1899). Also, wild host plants in nearby fencerows and ditchbanks should be destroyed to reduce the source of outside infestaion. Insecticides directed toward the adults and applied just before the plants flower effectively reduce populations (Johnson and Mayes 1989, Metcalf and others 1962).
Gallery
 Photo by James Solomon, USDA Forest Service, Bugwood.org |
References
Solomon, J.D. 1995. Guide to insect borers of North American broadleaf trees and shrubs. Agric. Handbk. 706. Washington, DC: U.S. Department of Agricultural, Forest Service. 735 p.
