Feature: Attack of the Emerald Ash Border: MSU Scientists to the Rescue

            MSU scientists could prevent an exotic beetle from wiping out all our ash trees.

            The crack of a wooden bat hitting a baseball in the summer is as American as apple pie.  But that sound—and the ash bats that make it—is being threatened by a metallic green beetle whose sole purpose in life is to seek out, feed on and ultimately destroy the United States’ approximately eight billion ash trees.

            Known as the emerald ash borer (EAB), this exotic wood-boring beetle native to Asia was discovered and ultimately identified in southeastern Michigan in June 2002. Emerald ash borer is native to Asian countries, including China, Korea and Japan. It is not a major pest in those countries, probably because Asian ash trees have evolved and become more resistant. An estimated 20 million ash trees in urban, forest and rural areas of southeastern Michigan have already been killed by EAB. More than 800 million ash trees in Michigan alone are threatened by this invasive pest.

            Michigan State University researchers are instrumental in leading the fight against this pest, and if the fight is lost, it could spell the end for native ash trees, leaving bare streets, more sparse forests and heat unabated by leafy canopies.

            “Very little was known about the beetle at all, even in its native range in Asia,” says Deborah McCullough, MSU forest entomologist and a primary researcher studying EAB at MSU. “There was only a page and a half of information about it—in Chinese—from a book on forest pests.”

            A postdoctoral research associate at MSU, Houping Liu, translated the information. The Chinese scientist who wrote those paragraphs was contacted by federal officials concerned about the threat EAB posed in the U.S. The Chinese scientist said that his notes and data about EAB had been destroyed during the “Chinese Cultural Revolution.”

            This means that MSU researchers were starting from scratch—and all signs indicated that EAB had been here for a while. There had been reports of ash trees dying for unknown reasons for several years in the Detroit area before 2002. Now that the reason was discovered, subsequent surveys of ash trees in the six counties surrounding Detroit by the Michigan Dept. of Agriculture and other state and federal agencies showed roughly 5 to 7 million ash trees infested, dead or dying from the pest. The unique S-shaped feeding pattern of EAB larvae under the bark as well as the tiny, D-shaped adult EAB exit holes from the bark told the tale.

            “It is generally believed that EAB came to Michigan and Canada through solid wood packing material, such as pallets or crating associated with cargo coming into Detroit,” McCullough says. “The beetles infested street and landscape ash trees in the Detroit area, many of which had been planted to replace elm trees killed by Dutch elm disease in the 1950s and ‘60s. Ash trees in parks, woodlots and along rivers and creeks were also affected by the pest.”

            Genetic studies done at MSU on the origin of the EAB found in infested states also point a finger toward China.

            “We’re working with EAB specimens from Michigan, Ohio, Indiana and Ontario in North America,” says Alicia Bray, an MSU entomology doctoral student working on the project. “We also have specimens from six populations in China and three populations in South Korea, and a single specimen from Japan. So far, Chinese EAB specimens are the most similar to the North American EAB.”

            Once discovered, scientists quickly realized that EAB had been around for quite a while, undetected. But how long? To figure it out, MSU post-doctoral research associate Nathan Siegert is using dendrochronology—the study of tree-ring patterns—to determine when individual ash trees died from EAB and, in some cases, when they became infested. So far, the data show that EAB was established in southeastern Michigan at least 10 years before it was identified. Siegert’s work has also been used to help determine when several infestations outside the Detroit area occurred.            

            “We’ve been able to determine that nearly all of these isolated outlier sites are a result of EAB being introduced to the area by either infested firewood and logs or infested nursery trees before anyone knew about EAB,” Siegert says. “What we’re discovering can be used to determine how quickly EAB populations increase in size and start to disperse in a given area. Our goal is to reconstruct the spread of EAB to predict how far and how quickly it’s likely to move, which will ultimately help us more effectively manage this invasive insect in other parts of North America.”

            Since the EAB infestation has at least a 10-year jump on its discovery date and the pest has subsequently been found in Ohio, Indiana, Illinois, Maryland and Canada, finding a way to detect the beetle’s whereabouts is critical.

            “The EAB larvae’s feeding is what kills the ash tree,” McCullough explains. “When trees are heavily infested you will see D-shaped exit holes left by emerging adult beetles, larger holes left by woodpeckers foraging on the EAB larvae, and dying branches. But when a tree has been infested for only a year or two, it often has no external symptoms of infestation. Right now our best method in finding EAB is to sacrifice an ash tree by girdling it [stripping a 360-degree section of bark from the tree, then smearing sticky material above that area to catch EAB and other insects], and that is very time- and labor-intensive.”

            A girdled ash tree emits high levels of various volatiles, which are aromatic signals that lead EAB to it. Therese Poland, an entomologist with the U.S. Dept. of Agriculture Forest Service and scientists from the Canadian Forest Service, showed that EAB antennae react to certain volatiles in ash trees. Using volatiles in traps rather than living trees could provide an easier, less costly and less time-intensive method to find EAB in areas where it has not yet been detected. McCullough, Poland and scientists from other agencies are also working together on trap designs that work with the lures to attract and capture adult beetles.

            “For example, adult EAB have been shown to be attracted to purple, so now our traps all involve purple-colored panels,” McCullough says. 

            One of the biggest fears is that EAB may infest other species of trees. MSU research has found that EAB are rather finicky and hard to fool.  If they can’t live on an ash tree (Fraxinus spp.), they’re not too interested in hanging around.            

            “We’ve done no-choice studies in the laboratory with EAB beetles caged in clear plastic boxes with various tree species, such as black walnut, Japanese tree lilac, American elm, hickory, hackberry and elm hybrids, which are all related in some way to EAB’s native host species in Asia and could potentially attract EAB,” says Andrea Anulewicz, MSU entomology research technician, whose study on EAB host preference was done as part of her graduate work with McCullough. “The studies show that EAB are host-specific—they prefer only ash trees. Unfortunately, they grew and developed on all species of ash we tested. We expect that virtually all North American ash species will be vulnerable to EAB.”

            Anulewicz took this study a step further by putting EAB in cages surrounding live trees to see if live trees of various species were more appealing than cut limbs. It didn’t make any difference—an ash is an ash, and that’s what EAB want.

            Saving ash trees from EAB is an ongoing fight. The larvae are protected by the tree’s bark, and because the adult beetles are so small, are green like the tree and live high in a tree canopy, it is difficult to find them, so insecticide sprays are not always a good choice, especially for large trees. Methods such as injecting trees, pouring insecticide drenches around tree roots, and biocontrol methods—such as predatory insects and naturally derived insecticides—are being studied at MSU.

            “What we know right now is that ash trees must be treated each year with insecticides if they are to fight EAB,” says Dave Smitley, MSU entomologist. “Homeowners who are facing the decision on whether to treat their ash trees must weigh factors such as the level of infestation, the size and health of the tree, and if it is economical to treat the tree every year.”

            One positive outcome that has come about from the battle against the EAB beetle is the high level of cooperation and collaboration between the Big Ten universities in infested states and state and federal agencies involved in the EAB program. Communication and outreach are very important when dealing with an invasive pest, and a communications team consisting of representatives from the aforementioned groups has cooperated on numerous projects, such as EAB Awareness Week in Michigan, Ohio and Indiana; development and dissemination of materials and resources; and public meetings and media blitzes to get the word out. MSU Extension and the Master Gardener network have proved a great asset in educating Michigan’s residents, community leaders and governmental officials about the seriousness of the problem, and other state universities’ extension services and Master Gardeners are following suit. The national multi-state Web site, www.emeraldashborer.info, is housed and managed at MSU.

            “If we lose all our ash trees, we lose a significant forest and urban forest resource in North America,” McCullough says. “Residents and municipalities in affected states have already spent millions of dollars replacing dead and dying trees. The ecological impacts of widespread ash mortality in forests are unknown at this point, but are likely to affect a variety of ecosystem processes. This is a battle worth fighting. The lessons we learn from this invasive pest could be applied to the next invasive pest. It’s not a matter of if—it’s a matter of when this will happen again. Foreign trade means we trade more than just consumer goods.”

            For more information about emerald ash borer and additional research being done, visit emeraldashborer.info.

            Robin Usborne, ’80, received her degree in Agriculture and Natural Resources Communications. She has worked as a communications manager in the College of Agriculture and Natural Resources for nearly 15 years.

HOW YOU CAN HELP STOP THE EAB SPREAD

            The emerald ash borer is spread mainly by human movement of EAB-infested firewood.  This is one of MSU’s most important research findings.  Most people cannot tell the difference between ash and other hardwoods. Because EAB larvae are underneath the bark, most people are not aware that it is there. When EAB-infested firewood is transported to campgrounds, cottages or other recreational destinations, there is a good chance those areas will become infested with emerald ash borer.

            Protecting our natural resources for our and future generations is important. Keep pests like EAB out of forests and woodlands by leaving your firewood at home and buying from local vendors at your destination. If you do bring it, burn it all before you leave. 

            For information, visit emeraldashborer.info.

MSU BATTLES BIO-INVADERS

            The work to stem threats against Michigan’s environment and economy is never-ending at MSU, where researchers and specialists work with state and federal government agencies, other universities and partnering organizations to understand and control invasive plants, animals and pathogens. 

            On-going MSU efforts against invasive threats include:

• Great Lakes Invasive Species Initiative: A multidisciplinary program to integrate research, outreach, regulatory and teaching campus-wide and provide access to this expertise (invasivespecies.msu.edu).
• Michigan Sea Grant: A joint program of MSU and the University of Michigan to promote greater knowledge of the Great Lakes through education, research and outreach.  Michigan Sea Grant undertakes extensive research and outreach in aquatic invasive species (miseagrant.umich.edu).
• Partnership for Ecosystem Research and Management: A partnership between MSU and the Michigan Dept. of Natural Resources to identify significant ecosystem problems and conduct research toward solutions (fw.msu.edu/PERM).
• MSU Integrated Pest Management (IPM): IPM offers management tools to safeguard farm and environmental health through applied research and research-based education (ipm.msu.edu).
• Environmental Science and Policy Program: A program facilitating interdisciplinary science focused on environmental issues (environment.msu.edu).
• MSU Extension (msue.msu.edu) and the Michigan Agricultural Experiment Station (maes.msu.edu) provide outreach and research focused on a wide variety of invasive species. 
• Other efforts include the Michigan Invasive Plant Council (forestry.msu.edu/Mipc/Index.htm), Purple Loosestrife (miseagrant.umich.edu/pp/index.html), Hydrilla (miseagrant.umich.edu/ais/hydrilla.html), the Multi-Colored Asian Lady Beetle (ipm.msu.edu/asianladybeetle.htm) and the Garlic Mustard Project: (ipm.msu.edu/garlicmustard.htm).