May 5, 2011
Dr. Ken Raffa, UW-Madison (608) 262-1125
Andrea Diss-Torrance, DNR (608) 264-9247
Experimental Release of Stingless Parasitic Wasps May Help Wisconsin Control Emerald Ash Borer
MADISON – Tiny stingless wasps the size of a grain of rice may someday play a role in controlling the emerald ash borer (EAB) infestation in Wisconsin. The invasive pest has killed millions of ash trees since its discovery in Michigan in 2002.
EAB was accidentally introduced from China within shipments of imported products. It is not a pest in Asia, where it only lives in dying trees, because ash trees there evolved with it and so healthy Asian ash have effective defenses. Unfortunately, there is no evidence of resistance in our ash species.
This spring, scientists with the University of Wisconsin – Madison, the DNR, and USDA-APHIS will introduce three species of stingless parasitic wasps that prey almost exclusively on the ash-killing beetle in a cooperative project. Emerald ash borer was first discovered in Wisconsin near the Village of Newburg in 2008. Since that time, EAB has shown up in Cudahy, Oak Creek, Franklin, West Bend and Victory, and has been trapped in Green Bay and Kenosha.
A Wisconsin Department of Natural Resources grant will help fund the research for the next three years.
Researchers plan to release two species of stingless wasps sometime in May and the third species later in the summer. The releases are timed according to specific weather conditions and will all be done at the Riveredge Nature Center near Newburg. All three stingless wasp species are native to China and are natural predators of EAB in the beetle’s native range.
The two species that will be released in May parasitize the larval stage of EAB – when the insect lives under the ash bark. They insert their egg-laying appendage (ovipositor) through the outside of the tree and then lay their eggs on the surface or inside the EAB larva. The stingless wasp species that is scheduled for release later this summer parasitizes EAB by depositing its egg inside the egg of the emerald ash borer.
“This experiment will help our understanding of the potential these wasps that may have as part of our attempts to reduce the spread and impacts of the emerald ash borer in Wisconsin,” said Dr. Ken Raffa, UW Madison professor of entomology. “Biological controls, such as these stingless wasps, can be an important component in an overall management strategy that also includes quarantines, education, and chemical treatments. These wasps have undergone intense scrutiny by the USDA to safeguard against harm to native species. So far, 180,000 wasps have been released in 9 states, including Michigan, Illinois, and Minnesota.”
“These tiny, stingless wasps pose no threat to people,” said Andrea Diss-Torrance, DNR forest entomologist. “They do not seek shelter in homes or other buildings as they all overwinter inside their host, EAB, under the bark of ash trees. As adults, these wasps are focused on finding EAB to host their offspring and so stay close to EAB-infested ash trees. Because they are so tiny and at work in the canopy of ash trees, most people will never see them. In fact, it is very hard even for trained entomologists to find the adult wasps in the field. To verify if our introductions are successful, we will have to peel the bark off of EAB infested ash and look for parasitized EAB larvae”
“The effectiveness of these stingless wasps against EAB is uncertain, yet it is clear that reducing EAB populations has a better chance of success when many approaches are employed,” said Jane Cummings-Carlson, forest health specialist with the DNR. “Extensive research conducted by the USDA shows that they are highly selective in going after EAB, so there is some hope that they may eventually be used on a wide scale to help reduce EAB populations, especially in Wisconsin’s forests where there are more than 700 million ash trees. It is very important that we explore every tool available to reduce the ecological and financial impact EAB will have on our urban and rural forests,” said Cummings Carlson.
“It will take some time, roughly five years, before we can assess the potential of these stingless wasps for affecting the population of EAB,” continued Cummings-Carlson. “If it does prove useful, it would be most effective in areas of known infestations since the stingless wasp needs the beetle to complete its life cycle. Cold-hardiness tests indicate the stingless wasps are winter hardy enough to survive from season to season in our climate.”
Nature is already lending a hand when it comes to reducing EAB populations. Native woodpeckers are often attracted to the abundant source of larvae in infested trees. One of our native ground-dwelling stingless wasps feeds exclusively on beetles within the same family as EAB. And in Michigan, scientists recently discovered an entirely different species of native non stinging wasp that preys upon EAB larvae. However, it is clear from the devastation that these agents are not adequate. As with tree defense, the natural enemies that evolved with EAB in China are more effective.
“Key to helping reduce the population of EAB in Wisconsin and in North America as a whole will be finding ways to combat the beetle across large tracts of land,” Cummings-Carlson said. “Currently, our insecticides work well to protect urban trees but are not practical in the forest setting. We really need an effective biological control to help us preserve our native North American ash forests.”
“Riveredge looks forward to this exciting partnership with the DNR and researchers from UW-Madison and we’re honored that they chose Riveredge as the release area,” said Patrick Boyle, executive director of the Riveredge Nature Center. “We all greatly hope that this project yields some positive results that we can share with the community.”
The emerald ash borer is a metallic green beetle about the size of a cooked grain of rice. It was introduced to North America in early 1990s in the Detroit area and has since been responsible for the destruction of millions of trees across 15 states and Canada. It attacks only ash trees.
For more information about EAB in Wisconsin, visit www.emeraldashborer.wi.gov or call 1-800-462-2803.
EDITOR’S NOTE: The timing of the release of the two larva parasitoids is based on a number of climatological factors and is inherently impossible to predict with great accuracy. One of the factors is the Growing Degree Day (GDD) temperature. The others include rain, wind, and daytime temperature. If you are interested in covering the release of the first two species of wasps, we will do our best to notify you of the release with as much lead time as possible. This may only be a day or two at the very best. Please submit your name and email address to Michael.Skwarok@wisconsin.gov. A mass email notice with directions to the release site will be sent when a release date is imminent.
Riveredge’s Response to the Emerald Ash Borer Challenge
The Emerald Ash Borer (EAB), a non-native invasive beetle, was discovered on Riveredge property in January, 2009. This did not come as a big surprise since the first documented cases of EAB in Wisconsin were found less than a mile away in Newburg in August, 2008. Authorities believe that, based on the extent of that infestation, the EAB has been in the area since at least 2004. That means the green menace has had ample time to spread throughout this and other surrounding counties.
Riveredge has become a showcase for demonstrating to other property owners the various methods used to detect and deal with the EAB. During the
summer of 2009, the Department of Agriculture, Trade and Consumer Protection (DATCP) placed purple traps of various sizes and shapes on the property. The traps were made out of thin, corrugated, purple plastic coated with different sticky, non-toxic substances used to lure the ash borers to them. Similar traps were placed in other parts of the county and state. If you see a trap in your area it doesn’t mean that EAB are in your neighborhood. The traps are simply used to determine if EAB are present and if so in what quantity.
Dr. R. Chris Williamson, from the UW- Extension in Madison, also conducted a study here the summer of 2009. Williamson and his grad students applied 14 insecticides on 140 trees of different ash species and age classes. The insecticides included soil-applied systemic insecticides, trunk-injected systemic insecticides, systemic basal trunk sprays and protective cover sprays which were applied to the trunk, branches and foliage. The subject trees will have to be monitored for a number years to determine the effectiveness of the insecticide used. They can only be used to protect the trees from EAB not eradicate it from a tree that is already severely infested.
A study initiated by Jane Cummings Carlson, forest health coordinator for the WDNR, in June, 2009 involved creating five EAB “sinks” near our west entrance. Each sink consisted of a cluster of one control and three girdled ash trees. The clusters were located within 50 feet of an existing trail to allow easy access and removal. The dying, girdled trees emitted a scent which drew in emerald ash borers that were looking for brood trees. These girdled trees were cut down and hauled out using Percheron horses on February 20, 2010 during a small-scale logging demonstration. Samples from each of the tree clusters were examined by DNR experts to determine their degree of the infestation. Over 2,000 board feet of ash lumber was cut here that day. The wood is being dried and will be used for projects at Riveredge. Some of it may be donated to other local groups for special projects. The bark was chipped and used on our the trails that summer.
In July 2010, the WDNR installed a mobile colony consisting of six nests of Cerceris fumipennis
at Riveredge. This wasp is not known to sting or bite humans. It is a solitary ground-nesting wasp but the nests are clustered together in colonies. Throughout the wasp’s flight season in July and
August the female stocks her nest with native buprestid beetles, as well as the emerald ash borer. For this reason this wasp was used as a tool for the ‘biosurveillance’ of EAB. The surveillance work involved observing female wasps as they returned to their nest with prey. Covering nest entrances temporarily confused incoming prey-ladden female wasps, and made it possible to identify the prey carried by each female. Throughout the wasp’s flight season the females provisioned their nests with an average of two beetles per day. When EAB were collected by one or more wasps in the colony, the flight time(s) of the successful wasp(s) were used to calculate the wasp’s maximum foraging range. This information was then used to confirm the maximum foraging range of EAB-carrying wasps.
During the winter of 2011 three of Riveredge’s neighbors joined together to have a managed timber sale. A forester from the WDNR identified the ash trees to be removed. A private contractor was then hired to do the logging. Proceeds from the timber sale were used to reimburse the contractor. Riveredge is considering a low-impact harvest of trees that pose a hazard to people and buildings.
With the help of a forester, we will also collect seeds from 6 trees each of three species of ash found on the property. The seeds will be sent to a seed bank for future use once EAB has diminished in the area. The mother seed trees will most likely be treated with an insecticide to insure their survival for at least a few more years. Dr. Chris Williamson will continue his research by reapplying a variety of insecticides to the 140 ash trees he treated back in the summer of 2009 with the hope that these trees may survive infestation.
Finally Dr. Ken Raffa from the University of Wisconsin – Madison is preparing to release three species of non-stinging parasitic wasps in a control plot on the other side of the river. If the wasps survive and reproduce they’ll help control the EAB population at Riveredge in the coming years.
Week of May 24th, 2010:
Emerald Ash Borer Week
The BugLady tries to inject a dose of humor/irony/attitude into her insect biographies, but there’s nothing funny about today’s Bug o’ the Week, the invasive and highly destructive Emerald Ash Borer (EAB). True, the EAB (Agrilus planipennis) didn’t ask to come here, and the dynamics of its expansion/explosion into uncharted, tasty, and predator-free territory follows the pattern of many previous invasive species. But, the BugLady is a lifelong fan of ash trees, so this one is personal.
’s first EAB infestation was discovered in the summer of 2008 on property adjacent to Riveredge Nature Center, just three miles from the BugLady’s home. EABs had been nibbling at the state’s north and south borders for several years, and their leapfrogging of several counties into Ozaukee County was a surprise. Since that date, they have been found in elsewhere in the southern half of the state (go to http://www.emeraldashborer.wi.gov/
and click on the link labeled “Map”).
Originally from Asia, the beetle was first discovered in the Detroit, MI area in 2002. It had probably hitched a ride into this country as much as 10 years earlier. Its strong flight typically allows it to increase its range by a mile or two per year, but it doesn’t have to depend on its wings to travel, since people have been doing the heavy lifting for it. The EAB has traveled hidden in shipments of ash tree products, from nursery stock to firewood to pallets, and it has now spread from Lower Michigan to Pennsylvania, Indiana, Ohio, Illinois, New York, Kentucky, Missouri, Maryland, Minnesota, Virginia, West Virginia and two Canadian Provinces. Almost all of the northeastern quadrant of the US.
Named for their green coloration, EABs are in the Metallic Wood Borer family (Buprestidae), a group of often-iridescent, sturdy-looking, bullet-shaped, short-legged, beetles whose thorax and stiff wing coverings look pitted and tough. EABs are about one-half inch long and an eighth of an inch wide. Not all ash borers are created equal; the native red-headed ash borer is in a different beetle family and is not a pest of healthy trees.
The EAB, which feeds only on members of the Ash family, is a grave threat to Wisconsin’s landscape. In the nearby Cedarburg Bog, for example, white ash grows in upland areas, and black, red and green ash are common in the wetter swamp hardwood and conifer swamp areas. The same inaccessibility that makes the Bog such valuable habitat for plants and animals makes comprehensive pest-control very difficult. At Riveredge, some 30% of the woodland trees are ash. Sources estimate that since 2002, 15 to 40 million North American ash trees have been killed by or are dying from EAB (most experts lean toward the higher number). To grasp its potential impact on Wisconsin, consider that the DNR estimates that there are more than 700 million ash trees in Wisconsin forests, and about 5 million more in our towns and cities. On its home playing field in Asia, the EAB is uncommon and ash trees can fend off an attack, but North American trees have no natural resistance.
Unlike Dutch Elm disease, a beetle-spread fungus disease that killed the majority of American elms, the damage done by the EAB is mechanical. The larval ash borers (grubs) tunnel and feed in the cambium and phloem just below the tree’s bark, blocking the flow of water and nutrients, and starving the tree’s crown. Their twisty tunnels are called galleries. Once infested, a tree is doomed, usually dying from the top, down within a few years. Dying trees often put up brushy new growth around the base of their trunk in an attempt to survive. Unlike their destructive offspring, adult EABs dine harmlessly on ash leaves.
Eggs are laid in crevices in tree bark, and when the larvae/grubs hatch out, they bore down through the bark into the nutritious cambium. There they feed until they’re about an inch long in mid-fall. They appear to overwinter as larvae under the bark and pupate in spring. Adults emerge by late June, exiting through a characteristic “D” shaped opening in the bark. Adults are active during summer but are gone by September. It’s unclear whether they live one or two years.
Woodpeckers make an occasional meal of the EAB, but it has no real enemies in this country. A few alien parasitic wasps are being tested as potential biological controls. When an infestation is discovered, quarantines on the movement of ash products, especially firewood, are imposed. Some states have tried destroying all ash trees, infested or not, within a certain radius of where the beetles were found, but this tactic has proved both unpopular and unsuccessful. There are a number of insecticides that show promise in preventing or treating an infestation. Since they are systemic and rely on being circulated via the same channels the larvae are interrupting, success in treating an infected tree is “iffy.”
This summer 8,700 large, purple sticky-traps will hang from trees in 71 of Wisconsin’s 72 counties. They are not a tool to control the beetle, they are an attempt to discover where the EAB is. They are baited with oil from the mankua tree, which smells like an injured ash tree. Last year 279 traps were deployed, and only one EAB stuck. The BugLady thinks this is a phenomenal opportunity to do general surveys of Wisconsin insect fauna and wishes that legions of entomologists were being deployed to record the non-EABs that meet their end on a purple sticky-trap.
About the pictures. If the EAB adult and larva look like they might just have been poured out of small bottles of formaldehyde, there’s a good reason for that (Thanks, Mary). Also, out in Nature, the D-shaped exit holes do not come with tiny, red lipstick outlines.
Following closely on the heels of the EAB, of course, have been a number of “entrepreneurs” who misdiagnose infestations and sell bogus prevention, treatment and eradication services to worried land owners. Caveat emptor!
The BugLady wishes everyone a safe, happy and productive EAB Awareness Week.