After years of failed attempts to eradicate or at least lessen the effect of the pests by destroying infected trees, officials with the U.S. Department of Agriculture and the Maryland Department of Agriculture in Cheltenham are trying to cut off the problem where it starts: with insect eggs. To do so, they have enlisted the help of another east-Asian insect: “stingless wasps,” which are smaller than fruit flies and lay their own eggs as parasites in ash borer eggs, eventually killing the host.
Although the tiny wasps are not a native species, officials said they are confident they will not become invasive.
Officials deployed the first set of wasp eggs onto infected trees May 30. The emerald ash borer beetles are particularly aggressive compared with native wood-boring insects, laying 70 to 100 eggs each, eating through the interior of a tree as larvae and then feasting on its leaves as adults, they said.
Ash borers are widespread despite earlier eradication efforts, which involved the destruction of 27 square miles of trees in Prince George’s County, where the region was first infested in 2003 via a tree nursery shipment from Michigan.
Since 2003, there have been reports of infestations in Charles, Howard, Anne Arundel, Washington and Garrett counties.
Officials said the program costs about $300,000 each year. Prior eradication efforts had cost as much as $1 million a year.
Charles Pickett, an agricultural inspector at MDA, said that not only do officials anticipate the eggs being more effective in stopping ash borers, but they hope they will be more capable of surviving and producing an enduring population to fight the invasive insect down to a manageable level.
“Each wasp can produce 62 eggs,” Pickett said. “We just want to get it to an equilibrium to control the borers so they’re not killing everything. We have native redheaded and clear-winged ash borers, which have always been here, but they only affect trees, they don’t kill them.”
Jian Duan, a research entomologist at the USDA and lead scientist in the effort to stop the emerald ash borer, said the wasps were one of several species tested before release for their potential effectiveness against the ash borer, as well as whether they would cause any adverse effects of their own.
MDA’s Cheltenham facility grows ash borer eggs to send to a lab in Michigan, which uses them to cultivate the wasps for use in Michigan and Maryland.
“[This species of wasp] and the emerald ash borer evolved together for many years,” Duan said. “It will be very hard for the wasps to switch to another egg.”
Dick Bean, program manager for plant protection and weed management at MDA, said the wasp effort is one of the last options available for saving the ash tree in Maryland. Given the region’s abundance of waterways and Chesapeake Bay tributaries, more conventional pest control means such as crop dustings of pesticides were out of the question.
“There’s just nothing on the market that we can use, especially [in Prince George’s County] because of environmental reparation efforts,” Bean said. “Biological control is one of the last hopes we have. But there’s no silver bullet yet.”
Bean said the first batch of eggs should at least make an impact on the ash borer population. Officials will keep track of the effectiveness of the wasps, as well as the dispersal system used thanks to a postdoctoral study conducted in conjunction with the effort by the University of Maryland.