GREAT OUTDOORS: Parasitic wasps released to protect ash trees

In 2002, people began seeing lots of sick and dying ash trees in the Windsor/Detroit area. After some investigations by the U.S. Department of Agriculture inspectors, the cause was determined to be from an invasive insect called the emerald ash borer.This destructive pest was likely present in shipping pallets brought over from China since the early 1990s. The ash borers subsequently spread throughout North America, despite ash tree transport restrictions, quarantines and ash tree eradication programs designed to contain them.The illegal transport of emerald ash borer-infested firewood and nursery stock trees regularly jumped outside the quarantine borders. Infested woods adjacent to rest stops along major highways offered convincing evidence of this method of spread.Emerald ash borers have decimated the ash tree populations in most of the eastern states. They have more recently crossed the Mississippi River and are currently in over 40 states and provinces, including those first detected this year.According to the USDA, "In addition to its value to the timber industry and the forest ecosystem, ash was one of the most popular landscape trees because of its tolerance of a range of environmental conditions and resistance to pests." "Ash was the most commonly planted tree species used to replace elm trees decimated throughout North America by Dutch elm disease and for new residential and commercial developments."The estimated cost of treating, removing and replacing 37.9 million ash trees in urban and residential settings from 2009-2019 was estimated at $25 billion."In Ohio, ash tree species collectively made up between 10-12% of the upland forest population and closer to 50% in wetter soils, such as ditch banks and wetland margins before the invasion.With their natural spread restricted to a maximum of two miles by flying, I had hoped that the isolation of the Lake Erie islands would spare their abundant ash trees from the same fate.After I saw pickup trucks with firewood being loaded onto ferry boats, I asked Billy Market, co-owner of the Miller Boat Line, if they would turn them away to spare the island's ash trees.At the time, they were following emergency maritime safety protocols implemented by Homeland Security after the terrorist attacks of September 11, 2001, and he replied that they were too busy watching for people wanting to "blow up their boats" to worry about firewood.As I feared, campers traveling on the ferries to Middle Bass, Kelleys and South Bass islands brought firewood that was infested with live larvae and the insects quickly spread and killed most of the ash trees on the islands. Luckily, lots of seeds that have been deposited into the woods from the prolific trees have produced new generations of ash trees that will help perpetuate the species from imminent extinction, but mature trees are rare. After determining that no native insects would effectively prey upon emerald ash borers, three species of parasitoid wasps from their native ranges in China and one from Russia have been selected to date by the USDA to test for liberation into North America.So far, 6 million of these non-stinging wasps, that only prey on emerald ash borers, have been released into 29 states. They are being raised in the USDA Emerald Ash Biocontrol Rearing Facility in Brighton, Michigan.The Lake Erie Islands Conservancy's AmeriCorps intern, Adrianna Burghardt, a senior studying at the University of Dayton, led a project this summer to release three of the species into areas of high ash tree densities on South Bass and Middle Bass islands.The most recent study that was conducted in Michigan and several northeastern states showed that these parasitoid wasps are killing 20-80% of the emerald ash borers in ash trees up to eight inches in diameter.With fewer ash borrers infecting ash trees, they may be successfully regenerating in areas where the wasps were released.The release of these parasitic wasps gives some hope for restoring some of the ash tree population on the islands and elsewhere where emerald ash borers have decimated our local woodlots.