Natural Predators and an Emerald Prey

Woodpecker-Emerald Ash Borer

In Missouri’s natural rural forest stands, ash trees only comprise about 3% of total trees. This tree makes up a greater percentage of urban trees – 14% for trees lining residential streets up to 21% in urban parks. Visitors to the state’s parks are reminded not to bring firewood into the state from other states when camping out here and to burn whatever they obtain locally and not take it out of state when they leave. These measures act like a type of quarantine to reduce the likelihood of the insect’s arrival into any state employing similar measures.

Tiny Emerald Ash Borers (they are only 1/2″ long or about the diameter of a penny) have killed millions of ash trees since they were discovered in Michigan in 2002. The beetles in their larval form disrupt the flow of nutrients beneath the bark. Over time, they kill the tree. I believe I first became aware about the threat at our Missouri State Fair in 2012. We encourage and support a high degree of diversity for tree planting in our forest as a hedge against any potential insect infestation. In July 2008, a small Emerald Ash Borer infestation was discovered at a Wappapello Lake campground. That discovery put the potential threat in a nearby county to our own forest. Since then, the beetle has been detected in several other areas in the state.

Because the insect is a serious problem in states where it has been identified, concerned citizens and officials have looked for all the possible methods they might employ to eradicate the Emerald Ash Borer that is killing ash trees. Enter natural enemies of the Emerald Ash Borers. These include predaceous and parasitic insects and insect-pathogenic fungi. With the help of bird-watchers, researchers used information from Cornell University’s Project FeederWatch (for which my late mother in law was a long-time volunteer) and the US Forest Service to identify that the Red-bellied, Hairy and Downy Woodpeckers and the White-breasted Nuthatch populations grew in areas of known Emerald Ash Borer infestations. This was not an impact caused by birds migrating into the area but a result of local birds flourishing and successfully rearing families because they had happily discovered an abundant new food source. Fortunately, BOTH bird species are natives here in our Missouri forest and that is reassuring for our own ability to come through the latest threat with our forest still in a good condition.

According to Walter D Koenig from Cornell’s Lab of Ornithology, the birds “can depredate quite a surprisingly high percentage of Emerald Ash Borer larvae in some forests” but that “It’s unlikely that this would be enough to stop the invasion, but it could certainly slow it down, at least in some areas.” We should not discount the tenacity of the most predaceous species on our planet, human beings, to continue to look for every way possible to turn back the tide of the latest invasive species to drawn our concern.

The arthropod predators of insects and mites include beetles, true bugs, lacewings, flies, midges, spiders, wasps, and predatory mites. Insect predators can be found throughout plants, including the parts below ground, as well as in nearby shrubs and trees. Some predators are specialized in their choice of prey, others are generalists. Some are extremely useful natural enemies of insect pests. Unfortunately, some prey on other beneficial insects as well as pests. Insect predators can be found in almost all agricultural and natural habitats. Each group may have a different life cycle and habits. Although the life history of some common predators is well studied, information on the biology and relative importance of many predatory species is lacking.

While research has found that commercial chemicals can be effective in controlling emerald ash borer infestations, “you just can’t afford to do that in the woods,” said Andrea Diss-Torrance, a forest entomologist with the Wisconsin Department of Natural Resources. And some of us (this blog’s author and her husband definitely included !!) PREFER NOT to use chemicals on our land.

Chinese Stingless Wasp ~ photo credit  U.S. Dept of Agriculture

Chinese Stingless Wasp
~ photo credit
U.S. Dept of Agriculture

Two kinds of wasps are being used that will insert their egg-laying appendage through the bark and lay eggs in tunnels on, or in, emerald ash borer larvae. Once the eggs become larvae, they will eat the larvae of the beetle, Diss-Torrance said. Another species of wasps released at a different point in the seasonal cycle lay their eggs on or inside the eggs of the emerald ash borers when they are laying their eggs on the bark of ash trees. Once the larvae develop, they will eat emerald ash borer eggs.

The process will be invisible. “They are very tiny, and a lot of their work will be done inside or on the bark of a tree,” said Diss-Torrance. Entomologist Ken Raffa of the University of Wisconsin-Madison said that “these wasps have undergone intense scrutiny by the USDA to safeguard harm against native species.”

Sometimes, biological controls have interesting consequences. We have experienced the swarming of Asian lady beetles that will crawl into crevices of homes and that look alot like a native ladybug. These are believed to have first arrived in the United States in 1916. Southern farmers reintroduced them in the 1980s to control pecan aphids. We once captured the lady bugs emerging indoors here in Springtime and relocated them to a treasured replanted live Christmas tree that had developed an aphid infestation.

The wasps are reared in a US Animal and Plant Health Inspection Service laboratory in Brighton, Mich. To date, 180,000 wasps have been released in nine other states, including Michigan, Illinois and Minnesota under permits granted by the inspection service, an arm of the U.S. Department of Agriculture. The first wasps used in a field trial were in Michigan in July 2007. Tiny wasps have been used to control gypsy moth populations.

Traditional Potawatomi Black Ash Basket ~ Nancy Krogmann of Whitepigeon Baskets

Traditional Potawatomi Black Ash Basket
~ Nancy Krogmann of Whitepigeon Baskets

The Potawatomi Indians of Michigan have been on the front lines of the battle against the Emerald Ash Borer. Their native tradition includes making a cultural style of basket from Black Ash trees. For generations the Potawatomi Indians have used wood from Black Ash trees to weave baskets, teaching the skill to their young. For the tribe there is much more at stake than a side source of income. “Baskets made from Black Ash played a huge role in our tribe’s life and history. Back then, the baskets were like money. You traded for it, and got the things your needed to care for your family” says Jamie Brown a part-time basket weaver who is part Potawatomi.

She learned basket making from her parents. Her mother learned the skill from her uncle. So there are at least three generations of her family that have made these baskets. She adds that “It’s part of who we are. It’s cool to carry on the tradition and share it with the next generation.” The USDA Forest Service research team has discovered that the Potawatomi Indian’s traditional method of storing Black Ash logs by submerging them in rivers can effectively preserve the logs for basketmaking while simultaneously KILLING the Emerald Ash Borer larvae lurking under the bark which then prevents the emergence of adult beetles in spring. A study concluded that submerging the logs for 18 weeks during winter or 14 weeks in spring killed the insects and retained the wood’s quality for basketmaking.

Thus the arrival of the insect onto their lands was taken quite seriously by the tribe. While the Pokagon Band of the Potawatomi tribe has used insecticide on its trees in the Hartford and Dowagiac regions, they are participating in the introduction of wasps as predators in their battle against the decimation of their ash trees by the Emerald Ash Borer.

Rachel Carson with Silent Spring bookcover

There are many potentially invasive insects listed at the Missouri Dept of Conservation’s page for the Emerald Ash Borer. Interestingly, they are all types of beetles from Asian Longhorn to June Bugs to Lady Beetles and more. A healthy and diverse forest with a healthy and diverse wildlife contingent will help any forest to survive the occasional arrival of undesirable insect guests. As Rachel Carson pointed out repeatedly, graphically and so very well in her 1962 book Silent Spring – natural deterents to such threats are the best approach and chemicals should be used only sparingly or not at all because any lethal chemical will have impacts beyond the intended targets. We have noted that after a large swarming of Lady Beetles here that over the years the quantity has naturally diminished to a point where their presence is less disagreeable. Just like the weather, insects have natural cycles that will seek balance with their environment over time.

Often too, the role of the beneficial predators has not been adequately studied. The use of chemicals is motivated by profits and easy availability. However, surveys of agricultural systems give an indication of the potential number and diversity of predators in a crop. For example, over 600 species of predators in 45 families of insects and 23 families of spiders and mites have been recorded in Arkansas cotton. Eighteen species of predatory insects (not including spiders and mites) have been found in potatoes in the northeastern United States. There may be thousands of predators per acre, in addition to many parasitoids. Although the impact of any one species of natural enemy may be minor, the combined impact of predators, parasitoids, and insect pathogens can be considerable.

It is also worth noting that the efforts of bird-watchers truly make a difference in helping to advance science. According to Koenig, data from Project FeederWatch and similar efforts “play a critical role in almost any attempt to assess the populations of animals at large geographic scales as well as the ecological consequences of an invasion such as that of the Emerald Ash Borer. Given the increasing prominence of such phenomena, citizen science projects such as FeedWatch and eBird are likely to play an even greater role in the future!”

~ Information Resources

“Emerald Ash Borer Management” posted at the Missouri Dept of Conservation website –

“Emerald Ash Borers vs Woodpeckers (And Nuthatches) posted 07/21/14 by Meredith Mann at 10,000 Birds –

“Biological Control – Predators” posted at Cornell University – College of Agriculture and Life Sciences –

“Natural U.S. Predators Discover the Emerald Ash Borer” posted 08/21/13 at Wood Acres Tree Specialists –

“State to send wasp hit squad after emerald ash borers” by Lee Bergquist posted 05/05/11 in the Milwaukee-Wiscondin Journal Sentinel –

“Pokagon Band uses wasps to save its trees, tradition” by Landa Bagley posted 08/28/15 in the South Bend Tribune –

“Basketmakers’ Tradition of Storing Black Ash Logs in Water Effective in Killing EAB” posted 07/18/15 in Native News Online –

“Submergence of black ash logs to control emerald ash borer and preserve wood for American Indian basketmaking” posted 06/27/15 by the USDA Forest Service Research Station in Lansing MI available from Wiley Online Library –;jsessionid=0AADC6B0F5BCE545F153F2306C8EB2DA.f01t02

Information about volunteering to participate in Project FeederWatch is avaialable at The Cornell Lab –

eBird uses global tools to report and make information about birds accessible – learn more at eBird –


Blog author ~ Deborah Hart Yemm is co-founder of
Yemm & Hart, a green materials producer