NC State Extension Publications

Description and Biology

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The raspberry cane borer, Oberea bimaculata, is a small, slender, black or very dark beetle with long antennae. It is 1/2 to 5/8 inch long. The thorax is yellow to orange and has two conspicuous spots. Females emerge from infested stems in late spring and summer and fly to the new growth. About six inches from the tip, they chew a line of holes all the way around the new growth and then they chew another line of holes about half an inch away. Between these rows of holes the beetles insert a single egg into the stem. By early July, eggs mature and a chunky, small, white grub hatches and begins to feed within the pith. As the grub bores downward it grows and becomes more slender. The stem dies and wilts above the area girdled by the beetle. The grub continues to bore downward and eventually reaches the base of the plant where sawdust and other waste products and pushed out of holes onto the ground. The grub usually overwinters in a cell excavated inside the plant close to the ground. The following spring the grub matures and molts into a pupal stage. A few weeks later, a new generation of beetles emerges from infested plants to continue the life cycle. Some grubs take two years to mature. Infested branches often die or they are so weakened that they break off easily.

Raspberry cane borer beetle

Raspberry cane borer beetles are slender and black with long antennae.

Raspberry cane borers chew two rows of holes in stems before ins

Raspberry cane borers chew two rows of holes in stems before inserting an egg.

Raspberry cane borers insert their egg

Raspberry cane borers insert their eggs completely into the stem.

Host Plants

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Raspberry cane borers have been reported from brambles and raspberry as well as azalea, rose, and even oak.

Raspberry cane borers usually cause the host stem to wilt.

Raspberry cane borers usually cause the host stem to wilt.

Residential Recommendations

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For control of raspberry cane borers, the plants can be sprayed with a pyrethroid insecticide in late spring after the new growth has matured somewhat to prevent the beetles from laying eggs. Pyrethroid insecticides are widely available in the garden section of big box stores. (It is probably not a good idea to spray tender new growth of trees and shrubs with insecticides as the leaves may be damaged.) Susceptible plants should be watched for wilting stems. Prune out infested branches as soon as wilting is noticed, and then burn or otherwise destroy them to prevent the beetle grubs from surviving to produce more beetles next year. It is probably a good idea to treat these plants again the next spring. Fortunately, these stem borers are sporadic pests so that treatment is probably not needed every year. If the problem is discovered one season and treated the following spring as well, the population of raspberry cane borers will probably abate naturally.

References

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For assistance with a specific problem, contact your local Cooperative Extension Center.

This Factsheet hs not been peer reviewed.

Author

Professor Emeritus
Entomology

Publication date: July 23, 2016
Revised: Oct. 11, 2019

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