It's bug versus bug in fight against invasive species

            The mixed hardwood forest on the edge of the town of Dalton in western Massachusetts looks healthy to the untrained eye, but the researchers from the University of Massachusetts who visited the site every few weeks last summer are anything but untrained. They quickly noted the small holes made in some trunks by foraging woodpeckers and distinguished them from the even smaller holes made by wood-boring insects. And staring into the canopy they observed that many of the trees were in the early stages of decline.

Consisting primarily of ash and red maples, the forest is owned by the nearby city of Pittsfield to protect its public drinking water supply. But it also serves as a living laboratory to test a variety of methods for controlling the emerald ash borer, an iridescent green beetle native to China that has killed hundreds of millions of ash trees in the eastern and central United States, Ontario and Quebec.

The invasive beetle was discovered near Detroit in 2002 and slowly expanded in all directions, reaching New York in 2008, Massachusetts in 2012 and New Hampshire a year later.

Spathius galinae, a parasitoid of emerald ash borer. (Jian Duan USDA)

While it hasn’t yet been found in Vermont or Maine, it is only a matter of time before trees there will also start dying. The beetle is expected to kill almost all mature ash trees in the region in the next decade or two.

But that isn’t stopping researchers from trying to control the invasive beetle and find a way to protect future generations of the trees from succumbing. While several trees in the Dalton forest have been injected with a systemic pesticide to test whether adjacent trees will benefit from the treatment, the forest is primarily the site of a series of biological control experiments to determine if the emerald ash borer’s natural enemies in the Far East might succeed at keeping the insect in check here as well.

As UMass research fellow Ryan Crandall wandered the forest, he carried with him two prescription medicine bottles capped with a fine mesh. Inside the bottles were coffee filters embedded with emerald ash borer eggs, and inside the eggs were the larvae of Oobius agrili, a tiny parasitic wasp that is one of several insects that scientists hope will do in the U.S. what they do in China – control emerald ash borer populations so native ash trees can continue to thrive.

Crandall and his assistant, Sebastian Harris, were seeking the perfect trees on which to hang the medicine bottles – ash trees that aren’t too far gone yet but that exhibit numerous woodpecker holes suggesting the trees are infested with emerald ash borers. Most of the larger trees they examined were already near death, but eventually the researchers selected a couple of smaller specimens and proceeded to hammer nails in their trunks and hang the pill bottles on the nails. Soon, they hoped, the parasitic wasps would emerge and seek out more emerald ash borer eggs in which to lay their own eggs.

Although Crandall and Harris spent just 30 minutes at the Dalton site, they were far from finished for the day. They had five more stops to make at similarly infested forests in Massachusetts, New York and Connecticut, where they left behind a total of 1,400 emerald ash borer eggs parasitized by Oobius agrili....

Continue reading the rest of this article in the fall 2017 edition of Northern Woodlands magazine.