Emerald ash borer-fighting wasps continue to be released

by | Apr 23, 2014

A cup full of Spathius wasps, just prior to release.

A cup full of Spathius wasps, just prior to release.

Almost a year ago, the emerald ash borer was detected in North Carolina for the first time. The invasive beetle, which bores into and kills ash trees, was found in four N.C. counties in 2013 (Granville, Person, Vance and Warren). From September to early November of last year, the N.C. Forest Service released wasps to combat the pest.  Releases were suspended in the winter because the wasps are not active in cold weather.

But, warmer weather is back and so is the wasp! Last week marked the first release of the wasps in 2014. Releases will likely continue weekly if environmental conditions are appropriate. To date, 31,425 female wasps have been released in North Carolina.

Last week also marked the first release of a Spathius agrili, a wasp species that we think will perform well in the warm temperatures of the South. In 2013, only a single wasp species, Tetrastichus plannipennisi, was released, simply because the seasonality was biologically appropriate for it.

Both wasps, which are native to China, attack the larva of the emerald ash borer as it feeds just under the bark of an ash tree. The female wasp drills through the bark and lays an egg on the beetle larva. When the egg hatches, it feeds on the emerald ash borer larva, eventually killing it. The wasps are small and are not capable of stinging people.

A third and final wasp species, Oobius agrili, will likely be released in North Carolina later this year. This wasp attacks the egg stage of the ash borer, so it must be released when the emerald ash borer begins laying eggs (in late spring and summer). A single adult wasp can parasitize 80 or more ash borer eggs!

All four counties where the emerald ash borer has been detected are under a state and federal quarantine. The quarantines regulate the movement of ash material, the insect itself and all hardwood firewood from regulated areas to non-regulated areas. For more information about the quarantine, visit the EAB Quarantine FAQ website, call 1-800-206-9333 (voicemail), or send an email to newpest@ncagr.gov.

As this invasive pest continues to bore ash trees to death, hopefully the wasps will begin to reduce beetle numbers and eventually contribute to control of the emerald ash borer in the forest setting. But as with most biological control programs, this is a long-term project, so only time will tell!