Northern Woodlands Magazine

citrus-farming industry. It cost just $1,500 to control the scale insect and eliminate the problem. Since then, hundreds of insects have been identified as possible agents for controlling a wide variety of exotic species, from aquatic weeds to forest pests.

When the emerald ash borer first became a problem in Michigan, and cutting down and grinding up the infested trees didn’t solve it, entomologist Juli Gould from the Cape Cod office of the USDA’s Animal and Plant Health Inspection Service (APHIS) went to China to learn about the borer’s natural enemies, most notably a variety of parasitoids – what Van Driesche described as “wasps that don’t sting and are about as big as a yellow jacket’s toenail” – that lay their eggs in or on emerald ash borer eggs or larvae. The wasp larvae flourish and the borers die.

Before the parasitoids could be released in the US, however, a lengthy series of “host specificity tests” were conducted to ensure that the parasitoids weren’t going to kill non-target native insects as well. That was the problem that surfaced in the early days of biocontrol efforts, when little attention was paid to the effect of the biocontrol agent on living organisms beyond the target pest.

In the early 1900s, for instance, a wide variety of non-native parasitic insects were released to control gypsy moth caterpillars. None worked effectively on that target pest, but one of those released insects, a tachinid fly, was later found to kill the caterpillars of many other moths and butterflies, including popular and beneficial species. So years of testing are now conducted in research laboratories to ensure that the biocontrol agents only prey upon the targeted invasive species. If the targeted pest is an insect, like the emerald ash borer, then numerous closely related native insects are tested to make sure the agent doesn’t also attack the relatives. If the target is an invasive plant, then as many as 100 related plants are tested. Several government agencies must sign off before the insects are released into the environment.

Oobius agrili and three other emerald ash borer enemies (Spathius agrili, Spathius galinae, and Tetrastichus planipennisi) were tested at an APHIS facility in Michigan, near where the infestation began. But two labs in New England also conduct these types of host specificity tests for a number of other biocontrol agents.

Biocontrol Agents

Security is high at the quarantine facility at the University of Rhode Island’s Biological Control Laboratory in Kingston.

Rather than keeping people out, the security is designed to
ensure that the insects stay in. Researcher Lisa Tewksbury
entered a security code to open the first door to the facility,
which led into a small, dark entryway she calls “the room of last
resort,” illuminated only by an overhead bug zapper she hopes
will attract and kill any insect attempting to escape. Once the
first door closed, she opened a second door into a prep room,
where she donned a white lab coat. It’s in this room where any
soil or plant material destined to be discarded is first cooked in
an autoclave or frozen for several days so surviving insects don’t
accidentally make it out alive.
Beyond the prep room, students in three brightly lit labs
provided food to various insects and experimented with methods
of raising them. In one, Hypena moth caterpillars, which were
found to eat only black swallowwort – an aggressive invasive
vine that may be harmful to monarch butterflies – chewed
on swallowwort leaves in Plexiglas cages while they awaited
government approval to be released. Another room contained
bins filled with stalks of Phragmites, an invasive reed that out-
competes native wetland plants. The Phragmites was being fed
upon by the caterpillar of a European moth that kills the plant
by burrowing into its stem and eating it from the inside out.

In an adjacent room containing chambers filled with lily plants, invasive lily leaf beetles were being reared for further testing. The blood-red beetle, which has wiped out populations of native and ornamental lilies throughout the Northeast, has been successfully controlled in Rhode Island and eastern Massachusetts by a parasitic wasp raised at the URI facility. The wasps have been shipped to partner researchers in Maine, New Hampshire, Connecticut, and Ontario for release in affected areas, and Vermont scientists recently requested their first batch of the wasps as well.

Richard Casagrande, the professor who leads the biocontrol research program at URI, said insects identified as potential biocontrol agents against invasive plants are tested under “no choice” conditions, meaning that the insect is provided with only one type of plant to eat at a time. “If they can live on it, they will; if they can’t, they die,” he said.

It usually takes years of host specificity testing and about $1 million in research funding before Casagrande is confident that an insect is safe to release. He said it took more than five years of testing of the control agent for lily leaf beetle, and even longer for the Hypena moth that eats swallowwort. When testing is complete, he petitions APHIS for a release permit.

A New Era?

Not everyone thinks biological control is the answer to the invasive-species problem. Dan Simberloff, a professor at the University of Tennessee, urges caution. He isn’t opposed to biocontrol on principle, but he doesn’t think it should be the first strategy employed to fight pests. “It’s often irrevocable if the species you introduce survives and doesn’t do the job,” he said. “There’s a good chance it may have impacts on non-target species.”