Friday, August 29, 2008
Biodiversity Corner: A non-stinging Carlisle wasp helps researchers detect wood-boring insects
This is a story about biosurveillance. It’s not the kind managed by the Department of Homeland Security, which is defined as a “system to provide early detection and warning
about biological events of potential national consequence” and is focused on disease outbreaks. This kind is about other biological threats to the environment and in this case it is about the use of one species to detect the presence of another. The story is also about the natural resources of Carlisle having value far beyond the borders of the town.
The central character
The star of the story is a native beetle-hunting wasp, Cerceris fumipennis. Like many members of the Sphecid family, of which there are around 1,100 species in North America, this is a digger wasp so-called because it burrows in the ground to make its nest. The females hunt for insect and spider prey which they paralyze (but do not kill) and place in their nests as food for their offspring. Within this large family, the members of the Cerceris genus are sometimes known as weevil wasps because some of them provision their nests with weevils. The star wasp in today’s story is one that targets beetles in the Buprestid family and is particularly fond of wood-boring beetles in the genus, Agrilus. It is a gentle wasp, at least from the human point-of-view. It doesn’t sting humans.
The Emerald Ash Borer (EAB) is an Asian species of wood-boring beetle which was first found in the U.S in Michigan in 2002 but it is spread.ing rapidly to other states, probably in infested firewood. It needs to be stopped, if possible, because it attacks healthy ash trees and kills them. So far, it is not known to be in Massachusetts. As with many introduced species, the local and regional flora and fauna have not evolved to keep it in balance. However, this beetle is an Agrilus species and therefore is potential prey for our beetle-hunting wasp. No surprise to learn that the EAB is green. It is also iridescent and like other Buprestid beetles is torpedo shaped.
U.S. Forest Service
Michael Bohne is an entomologist and an employee of the U.S. Forest Service working in the Forest Health Group in Durham, New Hampshire. Last year he attended a meeting where Philip Careless, a graduate student at the University of Guelph (Ontario, Canada), gave a presentation on his biosurveillance work in which he used the Cerceris wasp to detect the presence of the EAB. Bohne liked the idea. The EAB is a serious threat to forest health, and this program offered a significantly more practical, efficient and less-invasive method of detecting the EAB than any of the other options. Rather than using humans to try and monitor thousands of acres of forest, the humans can monitor the wasp, examine its prey, and release the wasp unharmed to continue its beetle-hunting life. The Forest Health Group in Durham, N.H. serves the needs of all six New England states and New York state. The first step in launching a regional biosurveillance program became one of education and in particular learning how to recognize the beetle-hunting wasp. For a training program, Bohne and his associates in the Forest Health Group needed access to an active colony and preferably one that was centrally located in the seven states. We are finally getting to the Carlisle part of the story.
Other vital characters
Dick Walton is a Concord resident and an experienced observer, documenter and provider of natural history services. Last year he video-taped the behavior of the beetle-hunting wasps at Foss Farm as they brought beetles back to their nests. He posted clips on the Internet. Thanks to Walton’s posting, Bohne found the Foss Farm site and thanks to Sylvia Willard, Conservation Commission Administrator, he was able to work out permission to bring people to observe the Foss Farm colony. All the logistics for the site were perfect, and it had a large enough colony with sufficient nests that multiple observers would not be waiting all day for a wasp to appear. They only needed the sun to shine – which in most years would not be a tall order in July and August.
Action at Great Brook
On July 30, 29 representatives from seven states met first at Great Brook Farm State Park for a classroom session and then reconvened at Foss Farm for some first-hand observation. To start they needed to distinguish the nests from those of other ground-nesting species. The entrance to the beetle hunter nest is perfectly round and about the size of a pencil. The sand that has been excavated is distributed more or less evenly around all sides of the hole. The hole goes straight down for about six inches before it turns and leads to chambers for stowing beetles. These wasps are not aggressive and since they don’t sting humans, you can monitor a nest entrance closely and safely. If the wasp is at home, you may see her black face with its three distinctive patches as she sits guarding the entrance or preparing to leave.
When I was there on July 30 and again on August 9, there were enough wasps in the air that I didn’t have to monitor nest entrances. In its flight, you can recognize the wasp by the single pale yellow band on the abdomen. The wasps were returning to their nests with a Buprestid beetle very firmly in their grasp. It was possible to get a close look at the wasp by first catching it in a butterfly net, scooping it up in your hand and then just holding the beetle. The beetle had been stung and paralyzed and was doomed to becoming fresh living food for the wasp larvae.
If any of the wasps had returned with an EAB instead of one of our native wood-boring beetles, we would have known that there were infested ash trees within 400 yards. If the beetle is on one ash tree in the ara, it will soon, if not already, be on the others. This would be the trigger for launching a control program.
Detection vs control
Even though the beetle hunter’s flight season runs from late June through August and each female stocks her nest with an average of two beetles a day, this is not enough to control the EAB. The role of the wasp is for detection. Careless is now testing the use of mobile colonies of beetle hunters that can be moved from site to site as needed for detection services just as honey bees are moved around to provide pollination services. The wasp colony nests in a giant sand box. The wasps fly and hunt only in daylight hours so they can be moved around at night. Wherever they find themselves when the sun comes up, they fly off and look for Buprestids.
First, “gregarious solitary wasp”; our wasp is solitary because there is one female per nest, but gregarious because the nests are clustered in groups or colonies of between 10 and 500 nests. Next, “cute wasp”; I never thought I would be putting those words together, but this wasp has a cute little face and since it doesn’t sting, you can hold it in your fingers and get acquainted. What about “good wasp?” Wasps have a bad reputation with humans because some are aggressive and sting but let’s not tar all species with the same brush. It should go without saying, but to be safe, before you decide to pick up a wasp in your fingers, make sure it is one of the kind that doesn’t sting. Finally, in the Forest Health Group, we have an “efficient government department!”
I’m grateful to Michael Bohne of the Forest Health Group at Durham N.H., and also Dennis Suoto and Colleen Teerling, who spent time at Foss Farm to teach me the basics. You can find more information on the beetle hunter and its prey at www.maine.gov/docs/mfs (search on beetle hunter);www.uoguelph.ca (search on Cerceris); Dick Walton’s video at www.rkwalton.com (click on Summer in the Sand, Solitary Wasps); Borror and Delong’s Introduction to the Study of Insects, by Charles A. Triplehorn and Norman F. Johnson; Insects, Their Natural History and Diversity, by Stephen A. Marshall. ∆
© 2008 The Carlisle Mosquito