of North America. Tese are habitat for innumerable marine creatures, including sea turtles, and are crucial nurseries for many important food fish. A keystone species is the seagrass, Zostera marina, which has been devasted over two centuries due to pollution, silt from development, fishing practices, and other human impacts. But there has been success in restoring this species and this important ecosystem. Since 1999, broadcasting more than 70 million seeds of Zostera into coastal lagoons in Virginia has led to the reestablishment of more than 3,600 hectares of previously lost seagrass beds. And as the seagrass returns, the entire habitat begins to improve: carbon and nitrogen sequestration increases, turbidity decreases, and production and diversity of animals returns, as noted in several recent scientific studies. As an example, the previously depleted bay scallops are returning to many areas—proof of concept that ecosystem recovery can work and gives people a financial reason to get on board. Restoring some species will require a


multifaceted approach. Until recently, one of the most common tree species in the Upper Midwest where I live has been White Ash, Fraxinus americana. Tis tree is the “host” of the weird Ash Bolete, Boletinellus (=Gyrodon) merulioides. Tis mushroom has long been a favorite in the late summer and fall. And not because of its edibility (it tastes gross), it’s just so weird and easy to find on lawns and in parks, beneath ash trees. It has a really interesting lifecycle. Long considered a bolete, its phylogeny was uncertain. What was certain was that it was mycorrhizal with White Ash; turns out, that’s not quite the case. Te mushroom actually is a symbiont of an aphid that lives as a parasite on the roots of the tree. Te fungus seems to afford the tiny bug some protection by growing around the insect and forming dark black galls on the roots of the host trees. For most of the year the fungus, thus, is quite small but come fruiting season, rather large mushrooms will crop up in large troops in close proximity to the trees. And as the trees decline, so goes this marvelous mushroom. Why are ash trees—pretty much all of them at risk? It’s because of a small


invasive beetle. Te Emerald Ash Borer, Agrilus planipennis, began setting off alarms in 2002, when ash trees in the Detroit area started mysteriously dying. Te adults feed on the tree’s leaves and lay eggs on the bark. Te larvae kill ash trees by burrowing through the bark into the phloem tissues that transport water and nutrients. Tey then transform into iridescent green beetles about the size of a grain of rice that fly off to attack other trees. After researchers identified the insect, which was accidentally imported from Asia, Michigan and USDA’s Animal and Plant Health Inspection Service (APHIS) imposed a quarantine that prohibited export of ash trees and wood from inside the infested zone. Biologists also began to set traps to monitor the spread of the beetle. But stopping the pest’s expansion has proven impossible. No doubt the beetle still gets moved around in wood and adults are decent fliers for beetles, traveling up to 10 kilometers and often go undetected in new areas for years. You can now find its devastation far beyond Michigan. Te borer has attacked and killed tens of millions of trees in at least 35 states, mostly in the eastern and central USA; it has also infested southern Canada. Te pest is not west of the Rockies … yet … but it’s only a matter of time. In 2017 the International Union


for Conservation of Nature (IUCN) declared the borer had caused six North American ash species to become endangered or critically endangered. A policy of containment has not worked. And so new strategies are being tried. At the start of 2021, the USDA announced it will try biological control, or introducing natural enemies of the borer. Te concept of biocontrol is to “mimic nature” and to have a predator or parasite that can keep the pest population in check, sustainably, without the constant use of poisons, etc. In the case of the borer, scientists have identified four species of parasitic wasps native to Asia that lay eggs in ash borer larvae or eggs. In a recent edition of the journal Science the USDA reported that “researchers have released the parasitoids on an experimental basis in 340 counties in 30 states. Tree of the wasps have established self-sustaining populations. At some sites the wasps have killed


20–85% of borer larvae feeding on ash saplings, and are helping young trees survive to reproductive age.” Tus the biocontrol appears to be working in some cases, notably in younger trees. However, the parasitic wasps appear less effective at protecting mature ash trees, perhaps because they can’t penetrate the thick bark to find borers. A second strategy of the USDA is


to breed borer-resistant ash trees that could be used to replant forests. But first you have to find those few resistant trees—like living needles in a dead haystack. Where to look? In towns and neighborhoods, where the plague first emerged, trees tend to lack diversity, as urban foresters tend to plant genetically similar strains widely, making street trees uniquely vulnerable to invasive pests. Trees growing in forests, by contrast, have had millions of years to mutate and mix genes into countless combinations. USDA scientists are finding that about 1 in 1,000 trees have some resistance and don’t die when under beetle attack. And from crosses among them, it is hoped, a fully resistant individual may be produced. (Although it’s taken decades, this has been successfully proven with elm trees that have been wiped out by Dutch elm disease, and American chestnut trees that were mostly eradicated by chestnut blight—both caused by invasive fungal pathogens). Te researchers are racing against time and unfortunately breeding for resistance is a slow process. Why not simply use modern techniques like genetic engineering? Te fact of the matter is that traits like insect resistance are typically controlled by many genes, not one— and in the case of ash trees, researchers don’t know which genes are important. Some may code for chemicals that kill feeding larvae or make wood less digestible; others may make leaves less detectable or palatable to adults. Several generations of breeding and selection will allow these genes to stack up over time, providing ever stronger defense. And there is reason for optimism. After only a few years, researchers have developed trees that are 80–90% resistant to beetles in trials. So there is a chance we could begin to see the progeny of these first hybrids being used to restore ecosystems in about 10 years, according to the USDA.


Fall 2021 FUNGI Volume 14:4 41


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