Rednecked cane borer
Agrilus ruficollis (Fabricius)
From: 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.
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).
Galleries spiral galleries in boysenberry. James Solomon,
USDA Forest Service. |
Damage infested raspberry canes with typical swellings. James Solomon,
USDA Forest Service. |
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