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BLACK TWIG BORER

Stephen Bambara, Extension Entomologist

CAUTION: This information was developed for North Carolina and may not apply to other areas.

BLACK TWIG BORER, Xylosandrus compactus (Eichhoff), Curculionidae, tribe scolytini, COLEOPTERA

damaged twigs
Black twig borers drill into the thin twigs of dogwood, grape, magnolia, live oak, laurel oak and many other plants from shade trees to orchids. Seemingly healthy plants are attacked. Infested twigs or stems will wilt and die back.  An infestation is more severe for a young tree. In North Carolina, this pest is more common in the southeastern and coastal counties.
 

BIOLOGY

The black twig borer is a very small (1/16 inch), shiny, black, cylindrical beetle.  Twig entrance holes are about 1/32 inch in diameter and usually found on the lower surface of the twig.  Eggs are extremely small, oval, white and translucent. Black twig borer grubs are white and legless. The body of young grubs is pointed at the rear.  Older grubs have a brownish heads and round tails.  The pupa is about the size of the adult and clearly shows the legs,wings and head.

Black twig borers introduce a fungus, Fusarium solani, into the burrow that produces a white fungal "ambrosia" on which the grubs feed.  The grubs apparently feed on the pith as well.  Development takes 28-30 days from egg to adult during the growing season.  Females begin laying eggs as the weather warms in Spring and will lay eggs until the weather cools in autumn.  Grubs are most numerous during the growing season.  This insect overwinters as an adult beetle inside the stems.  After females emerge from a twig, they usually bore into the next twig within 30 minutes.  The heaviest amount of beetle flight coincides with the time that dogwoods are flowering.  Most emergence occurs from twigs between noon and 3:00pm.

drawing of life stages
Males are flightless and do not leave the brood cavity.  (An unmated female produces only male offspring.)  Females sometimes bore into plants without laying eggs. Only single females infest small twigs (< 5/16 inch) and such twigs usually die. Branches up to 7/8 inch may be infested with as many as 20 females.  Such branches may die or form a canker around the infested area.  Cankers may be as long as nine inches.  Wilting symptoms usually appear just weeks after the first attack.  Females tunnel into a twig for 3/4 to 1 1/4 inches to reach the pith or to form a  small chamber where a loose cluster of eggs is deposited. The grubs feed on the ambrosia fungus cultured on the walls of the tunnels and brood chamber.  Pupation and mating takes place in the infested twigs.  New adults emerge through the entrance holes of the parent beetles.  Adults overwinter inside infested twigs.

CONTROL

Prune out and destroy infested twigs where practical.  Mulching, avoiding overfertilization, irrigating during dry weather and general practices that enhance the health of the plant will make them better able to withstand attacks.  Cold winters will also reduce spring populations.  When using one of the following pesticides, follow label directions carefully. Do not apply to wet bark. Homeowners have few alternatives for chemical control. A few pyrethroids in homeowner formulations with the target plant on the label may be used with uncertain result. 
Pesticide (Trade Name)
permethrin (Astro [nonlandscape], PermethrinPro, others)
(*Home Defense, *Home & Garden Insect Killer, *Bug-B-Gone Multipurpose Insect Killer Ready Spray, others)
bifenthrin (TalstarOne, Talstar Lawn & Tree, Onyx)
*Suitable for homeowner use.
Recommendations for the use of chemicals are included in this  publication as a convenience to the reader. The use of brand names and any mention 
or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination 
against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations 
and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any, chemical. For assistance, 
contact an agent of the North Carolina Cooperative Extension Service in your county.
Other Resources
© 2001 NC Cooperative Extension Service

ENT/ort-106
July 1994, J.R. Baker (Revised) Oct. 2001
Revised by: Stephen Bambara, Extension Entomologist, Sept., 2003

Web page last reviewed January, 2011 by the webperson.