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.
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
Dan Simberloff is cautious about using