Several species of insect borers infest brambles and can cause destructive crop damage in two different ways. One group of insects made up of three species of beetles primarily damage canes and are classified as cane borers. The second group comprised of one species of insect, a clear-winged moth, damages crowns and roots of plants and is commonly known as the raspberry crown borer. In both groups, the major damage is caused by the larvae or borers of these pests that tunnel into plant tissues.

There are three species of bramble cane boring beetles:

1. Raspberry cane borer, Oberea bimaculata
2. Red-necked cane borer, Agrilus ruficollis
3. Bronze cane borer, Agrilus rubicola

Both the red-necked and the bronze cane borers are also collectively called flat-headed cane borers (referring to the larval stage), as both species have nearly identical life cycles and similar looking borers. The raspberry crown borer, a Lepidopterous pest, Pennisetia marginata, is also known as the raspberry root borer. This insect should not be confused with the root damage caused by the larvae of three species of snout beetles that also damage strawberries (Oitiorynchus spp.–black vine weevil, strawberry root weevil and rough strawberry root weevil).

Raspberry Cane Borer

The adult is a slender, black beetle about 1/2-inch long with a bright orange thorax, which has two to three black spots. Characteristic of long-horned beetle adults are the long, black antennae. These insects require two years to complete their life cycle (see table below). The beetles appear in raspberry plantings in early June and may remain present until late August. The adults feed on the tender green epidermis of cane tips leaving brownish patches or feeding scars.

The female beetle uses her mouth parts to puncture stems to form two rings of drilled holes about 1/2-inch apart in a girdling fashion about six inches from the cane tip or lateral shoot. After puncturing, the female then deposits and egg into the cane pith between these rings. This causes the first observed damage of the wilting and blackening of cane tips and laterals in early June. Upon hatching, the larva, called a borer, burrows through the cane, reaching its base by the fall and the crown by the next summer. Often this severe injury will cause the infested cane to die or fall over before fruit matures the following season.

Control. In new growth, prune and destroy the infested portion of the stem or lateral a few inches below the wilted tip. Damaged canes and crowns or roots should be removed and burned during the dormant season. Sprays directed at adults are applied at late prebloom, just before blossoms open (refer to New England Small Fruit Pest Management Guide, available at the Resource Store at the UConn Office of Communications and Information Technology for recommendations). Also, eliminate any wild brambles near the field, which may be harboring cane borer-type pests.

Flat-Headed Cane Borers

Both the red-necked cane borer and the bronze cane borer burrow through the canes of raspberries, blackberries, and dewberries. The red-necked cane borer adult is about 1/4-inch long, with a reddish-colored thorax that contrasts sharply with its black head and wing covers (elytra). The bronze cane borer beetle is similar in appearance except for its iridescent bronze or coppery color and is somewhat smaller. The life cycle of the two species are nearly identical (see table below).

Adults are present from late May to early August. They feed along the edges of the leaves and are easily found on sunny days. Females deposit whitish, scale-like eggs along the bark of the new growth during May and June. Eggs are also inserted into young canes, usually within 10 inches of the base of the cane. They do not girdle the cane as the raspberry cane borer does, but later the tunneling of the borer causes a symmetrical swelling or gall to form. These canes may also weaken and may break off.

After hatching, the young larva enters the bark at the axil of a leaf stem. The borer then constructs a long, winding tunnel which spirals around the cane several times in the sapwood, then turns into the hardwood, and then deeper into the pith. By early August, the galls commence to form where the bark has been girdled, though sometimes no gall results from the injury. Once the tunnel reaches the pith, it straightens into a path through the pith. The larva is full-grown by fall, remains in the tunnel during the winter, and pupates in the spring during late April. Adults emerge in the summer beginning in late May. The swellings or galls usually have numerous slits and range in size from 1/2 to nearly 3 inches long on the cane.

Control. Remove all canes that show swelling and destroy them. Also, eliminate any wild brambles nearby which act as hosts for these pests. Insecticides are directed at adults only, and are applied at late prebloom just before blossoms open. Refer to New England Small Fruit Pest Management Guide, available at the Resource Store at the UConn Office of Communications and Information Technology.

Raspberry Crown Borer

The adult is a very striking moth, resembling a yellow jacket in color, with a wingspan of 1 to 1 1/4 inches and four or more bright yellow bands across the black abdomen. As with the raspberry cane borer, this insect also requires two years to complete its life cycle. Adults appear in early August and are present through most of September. Female moths can be seen during the day resting on the leaves near the edges.

Oval, reddish-brown eggs are individually laid on the undersides of leaves near the edge in late summer. After hatching, small white caterpillars move to the base of the canes. Here, they either excavate a small blister like cavity under the bark near the base of the stem or find a protected place in the bark to overwinter. The following spring, the larva enters the crown and the roots, but it usually tunnels into a new cane and girdles it before returning to the crown and root tissue. The second winter is spent in the roots. By the second summer, the crown area can be extensively tunneled with galleries and damaged. The whole crown may be hollowed out.

Damage from this serious pest can often be confused with root rot and wilt diseases. The first indication of injury is the withering, wilting, and dying of the cane foliage, often with half-grown fruit still attached. Damaged canes will often break at the damaged area when pulled, revealing the larva inside. In New England, swelling of the crown has also been observed. In severe cases, the infested plant may die. The crown must be dug and opened to find the larva infesting it.

Control. During the growing season, dying and girdled canes showing symptoms of infestation should be removed and destroyed. All wild brambles in the area should be eliminated. For insecticides, refer to the current version of the New England Small Fruit Pest Management Guide, available at the Resource Store at the UConn Office of Communications and Information Technology.

Table 1.   Life Cycles of Insects Attacking Canes, Crowns and Roots of Bramble Plants
		APR	MAY	JUN	JUL	AUG	SEP	OCT
Raspberry Cane Borer	Year 1			Egg in stem
			Adult-feeds on cane tips
		Pupa			Larva in cane			Overwintering larva in canes
	Year 2	Larva in roots and canes					Overwintering larva in roots and canes
		APR	MAY	JUN	JUL	AUG	SEP	OCT
Raspberry Crown Borer	Year 1	Larva in crown			Pupa	Adult
						Egg
						Larva in base of cane or            protected place
	Year 2	Larva in crown, roots and canes						Larva in roots (Overwintering)
		APR	MAY	JUN	JUL	AUG	SEP	OCT
Flatheaded Cane Borer				Larva tunnels in cane-swelling apparent by July and August				Larva in canes (Overwintering)
		Pupa in cane		Adult feeds on leaf, lays egg on bark
			Egg
		APR	MAY	JUN	JUL	AUG	SEP	OCT

By: Norman L. Gauthier, Cooperative Extension Educator, Entomologist, University of Connecticut

Originally published: Grower, Vegetable and Small Fruit Newsletter, Vol. 93-5, May 1993, pp. 1-4.  Updated November 2008

Reviewed by: Mary Concklin, UConn IPM. 2012.

The information in this document is for educational purposes only.  The recommendations contained are based on the best available knowledge at the time of publication.  Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension System does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.  The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.