Using a Wasp to Catch a Beetle: The Quest to Save Ash Trees



For nearly a decade, a tiny alien menace, a beetle known as the emerald ash borer, has been destroying some of the nation’s most iconic native trees. Now researchers are honing a new method that uses wasps to ferret out these invasive beetles. The technique could help prevent the spreading of the emerald ash borer, as well as benefit other imperiled plants in the future, both in the U.S. and abroad.

The emerald ash borer is a small, green beetle of the Buprestidae family, a group more commonly known as jewel beetles. Ash borer larvae feed on a tree’s cambium, the layer directly under its bark where water and nutrients are transported. Ten years ago, the first of these beetles was found in Michigan, accidentally brought from Eastern Asia by boat. This highly destructive insect has since spread to 14 other states and two Canadian provinces, killing more than 50 million ash trees in the process and causing tens of millions of dollars in property damage.

A map of emerald ash borer sightings

Commonly used as firewood and in furniture, ash wood produces more than 25 billion dollars’ worth of revenue annually for Eastern States. Ash tree decline doesn’t just hurt business; it severely alters ecosystems—ash trees can comprise up to 40 percent of the trees in certain areas of forests.

Figuring out how to dampen the emerald ash borer’s threat is complicated. Just finding it is a problem—most known surveying methods for this particular insect are expensive and ineffective. The beetles spend most of their time under tree bark, and their size and green color make them virtually invisible to people when they do venture out of their trees.

The good news is that scientists from various institutions have developed a new method of tracking the beetles based on a technique called bio-surveillance. Put simply, they found that in order to catch an insect, it helps to be an insect. Scientists discovered that a certain species of native wasp (Cerceris fumipennis) hunts only jewel beetles, including the ash borer, which it uses to feed its larvae. By identifying the types of jewel beetles wasps bring back to their nests, the researchers can get a handle on whether or not a forest’s ash trees are endangered. For example, if there are no emerald ash borers in a nest full of 50 jewel beetles, then a forest is considered free of infestation.

So what happens when they find an emerald ash borer? “Removing [emerald ash borers] from an area is not going to happen, sadly,” says Dr. Claire Rutledge of the Connecticut Agricultural Experiment Station, which is participating in the bio-surveillance research, “so what [we need] is management, to try and spare as many trees as possible, and also to cope with the number of resulting dead trees.” The first step is to quarantine the area. Then, the trees must be treated with insecticides. Since heavily infested trees have no chance of surviving, they must be cut down and removed to prevent the spread of ash borers.

Researchers are also using the wasp to survey resident beetle populations across the state as well as for other national and international environmental issues. With the success that it’s achieving now, it is very likely that bio-surveillance will become a common research method around the world.

*This post was updated at ~12:50 p.m.

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