Hunting wasps: a more sensitive tool for detecting emerald ash borer?

French entomologist Léon Dufour was amazed to open a Cerceris hunting wasp nest and find it packed with jewel beetles, another name for metallic wood boring beetles! That was more than 150 years ago but now that another jewel beetle, the emerald ash borer, has been wreaking havoc on millions of ash trees as it advances through the U.S. and Canada, scientists are looking more closely at Cerceris as a tool to detect emerald ash borer.

A metallic wood boring beetle, also called a jewel beetle. Beetles in this family are preyed upon by the hunting wasp Cerceris fumipennis. Photo credit; Steven Valley, Oregon Dept. of Ag.

The hunting wasp, Cerceris fumipennis. Phot credit; Johnny N. Dell.

 

Cerceris fumipennis is a hunting wasp that specializes on metallic wood boring beetles, the only wasp species to do so in eastern North America. This wasp with the funny name (fumipennis actually means smoky-wings) hunts metallic wood boring beetles and stocks them in its nest. Its nest, a hole that it has burrowed in the ground, is filled with paralyzed adult metallic wood boring beetles. If you search the nest carefully soon after the female wasp has provisioned it and sealed it, you will find that one of these paralyzed beetles will have a sausage-shaped egg tucked carefully on the thorax. This egg will hatch into a voracious grub and devour the beetles that its mother has stocked in its nursery.

Illustration of a paralyzed jewel beetle with the egg of Cerceris fumipennis attached to its thorax.

 

Being able to detect emerald ash borer early would help limit its spread. So far, detection efforts, including the use of baited traps and monitoring for declining ash trees, has proved inadequate. Usually, emerald ash borers are detected only after they have been established at a location, sometimes up to five years prior! Part of the reason is that infestations of emerald ash borer usually start high in the ash trees where it is very difficult for humans to look. As the population of borers builds, they move down the trunk of the tree. By the time it is at a level that we can easily see it, the tree is already on its way out and thousands of beetles have moved on to infest new ash trees.

But hunting wasps are uncanny at finding their prey. After all, the lives of their offspring depend on it. They know where to seek their prey and the heights of an ash tree are no barrier to them! It occurred to entomologist Dr. Stephen Marshall that monitoring nests of C. fumipennis near ash trees might reveal the presence of emerald ash borer. Sure enough, the wasps did bring adult emerald ash borers to their nest!

It is not perfect. Ash trees that need monitoring are not always near aggregations of nesting C. fumipennis wasps. The wasp, which can be found from Florida to southern Canada, prefers to nest in open sites with full sun. Hard-packed sandy soil with sparse vegetation is preferred by C. fumipennis. Baseball diamonds, unpaved parking spots, sandy roadsides, footpaths that are near ash trees are all places to look for nesting aggregations.

More complete information on Cerceris fumipennis, including identification and how to use them to monitor for emerald ash borer can be found at http://www.cerceris.info/.

If you would like help identifying nesting sites in South Carolina you can contact me at djenkins@scfc.gov.