A New Weapon in the Fight to Protect America's Ash Trees is Under Evaluation

USDA Blog Post:

Posted by Sharon Lucik, USDA, APHIS, Plant Protection and Quarantine, on May 21, 2014 at 5:30 PM

Photo of S. galinae by Jian Duan, Research Entomologist, USDA ARS Beneficial Insects Introduction Research Unit

May 18-24, 2014 is Emerald Ash Borer Awareness Week

In our efforts to preserve and protect American ash trees from the damaging and invasive emerald ash borer (EAB) beetle, APHIS is working diligently to find and implement solutions that have the potential to successfully conserve this beautiful natural resource. Spathius galinae (S. galinae) just could be that newest weapon in the arsenal.

The tiny stingless wasp, about the size of a typical mosquito, targets and attacks EAB larvae living under the bark of ash trees.  Crawling along the bark ridges and furrows, S. galinae somehow senses EAB larvae hidden below.  The wasp not only accurately locates its target, but also is able to determine relative size—showing preference for large EAB larvae.  Once a suitable larva is detected, the female wasp uses its long egg-laying organ (ovipositor) like a hydraulic drill to bore down through the layers of bark and deposit between 5 and 15 eggs on its host.  After the eggs hatch, the wasp offspring feed on the EAB larva, eventually killing it.  A new generation of S. galinae emerges in about 35 days.

S. galinae was collected from the Russian Far East region and is not native to the United States.  The wasp is a hardy parasitoid capable of surviving the severe Russian winters of the region in which it was first found.  This characteristic, along with its long ovipositor, make S. galinae an optimal fit for release in the northern EAB-infested States.  In addition, extensive studies indicate S. galinae targets only EAB, and does not attack or parasitize other native wood boring beetles, such as the bronze birch borer.

Before this potential new weapon is used in the United States, the U.S. Department of Agriculture (USDA) will prepare and publish an environmental assessment (EA) identifying the risks and benefits of releasing S. galinae. The EA will be published in the Federal Register to allow the public to review and submit written comments prior to any release. Issuing permits for the release of S. galinae is part of USDA’s responsibility in regulating biological control organisms.  If permitted, the release of S. galinae could occur as early as next year (2015) in EAB-infested states.

Another species of stingless wasp, Spathius agrili (closely related to S. galinae) was tested, reviewed and approved for release against the EAB in 2007.  This wasp has a similar life cycle as it also bores into the bark, lays its eggs on EAB larva and eventually kills it. Recent field studies, however, show that S. agrili, which is from China, is not establishing in the more northern states where EAB has infested ash trees.  Furthermore, with a shorter ovipositor, its ability to target EAB larva in large, thick-barked ash trees is compromised.

Two other species of parasitic wasps were approved for release in the fight against EAB in 2007. Although it is premature to talk about the wasps’ impact on EAB populations, 10 states have documented the wasps’ ability to establish a reproducing population.

Ash trees are an important natural resource in our urban landscapes and forests, and so far EAB is responsible for killing tens of millions of them.  However, as these small wasp warriors continue to spread and eventually level the playing field, we are optimistic the health of the mighty ash tree and its presence in North America will endure.