Sting like a wasp: Small wasps released to attack invasive emerald ash borer

by | Oct 9, 2013

Small wasps (bottom) are being released in north-central North Carolina to combat the invasive emerald ash borer (top).

Earlier this year, the emerald ash borer was found in North Carolina for the first time. Dead and dying ash trees are already found in four N.C. counties and the beetle is likely to continue spreading. This wood-boring insect, which is native to Asia, was found in Michigan in 2002 and has rapidly spread throughout the states, leaving tens of millions of dead ash trees in its wake. To date, 22 states have detected emerald ash borer.

The emerald ash borer is killing ash and taking names. It has the potential to kill all of the approximately 258 million ash trees in our state. Ash trees can be protected or helped to recover with pesticides, but the treatments must be applied to individual trees, must be reapplied after several years, and are not economically feasible for the forest setting. For these reasons, pesticides are a viable and recommended option for urban, landscape or otherwise valuable ash trees, but there is not much that can be done to protect the ash trees of our forests.

Can we save our ash? The answer to that question just might lie in the hands – or legs, rather – of a very small wasp. In September 2013, the N.C. Forest Service began releasing parasitoid wasps at sites in N.C. known to be infested with the emerald ash borer. These wasps, which do not sting humans, lay eggs in immature emerald ash borer larvae as they feed on tree tissue beneath the bark. When the wasp eggs hatch, the immature wasp larvae feed on the emerald ash borer, eventually killing it.

In areas of China, where the wasp is native, the wasps can kill up to 50 percent of emerald ash borer larvae, playing a major role in keeping the population of this beetle at non-damaging levels. The hope is that they can play the same role here, once established.

The wasps, which are reared and sent to the N.C. Forest Service by USDA Plant Protection and Quarantine, were subject to an environmental assessment before their release. They were found to have no significant impact on our native ecosystems or species. Sixteen states have already released wasps.

It will likely be a long and sawdust-filled battle, but releasing these wasps is the first step towards long-term, sustainable management of the emerald ash borer. In years to come, the success of these wasps will be monitored and we are all hoping for a happy ending.