Weevils vs. The Mile-A-Minute Weed

  • The mile-a-minute weed (Photo courtesy of the USDA)

Sometimes biologists fight foreign
pests with other foreign animals. But that
can be risky because it can create a bigger
problem than the one it’s supposed to solve.
Sabri Ben-Achour reports on one of the latest attempts to stop a weedy pest:

Transcript

Sometimes biologists fight foreign
pests with other foreign animals. But that
can be risky because it can create a bigger
problem than the one it’s supposed to solve.
Sabri Ben-Achour reports on one of the latest attempts to stop
a weedy pest:

On farms, backyards, and rights of way up the Eastern Seaboard a pointy leaved thorny
newcomer is becoming increasingly visible. It’s called mile-a-minute weed.

Bob Trumbule is an entomologist. He leads me through a stream valley north of
Washington DC where blackberries and small trees are being swallowed up by this
invasive vine.

“So now we’re getting into the mile-a-minute here. Basically what it does it, it’s an
annual vine, it grows up and over plants, it smothers them, out competes them for
sunlight, and weighs them down.”

The weed is native to Eastern Asia: China and Japan. It was introduced accidentally in
Pennsylvania in the thirties. From there, it’s spread to seven other states. It prevents new
trees from sprouting in forests. But back in Asia, it’s not a dominating species like it is
here.

Judith Hough-Goldstein is a professor at the University of Delaware.

“Part of the reason is because it doesn’t have anything that’s feeding on it. It’s gonna be
without its predators so it can out-compete other plants.”

Over several years, biologists searched for something that would eat the vine. They
found a tiny, black weevil in China. It feeds on the plant and lays it’s eggs there, keeping
things in check – in Asia.

“Here are the weevils. I’m gonna give you a glimpse of them here in the cup. They look
almost like little ticks. I’m gonna put them down here in the mile a minute weed patch,
and basically what they’ll do – they’re tough little guys – they’ll climb around and in the
past experience have started to feed almost immediately.”

Up close, they look like little anteaters, poking around the leaves with long snouts.

This may sound risky. There are lots of examples where similar approaches have gone
wrong. A parasite was introduced in North America to control gypsymoths. It attacked
native silkmoths. Mississippi catfish farmers used Asian carp to control algae. They got
loose and are taking over the Mississippi River system and threatening the Great Lakes.

And Trumbule admits nobody knows for sure exactly what might happen.

“Any scientist that might say otherwise is not being honest with themselves or the person
asking the question.”

But he says a lot’s been learned since the days when any scientist could introduce a
species on a whim. These days, exhaustive testing and federal permits are required
before anything is released.

That’s why for almost ten years Judith Hough-Goldstein has been trying to determine if
the weevil would eat anything else. Tests were conducted in a U.S. Department of
Agriculture ‘quarantine facility’ with sealed windows and its own re-circulated air supply.

“So what we found was that, in fact, this particular weevil is extremely host specific. The
insect has evolved to depend on the plant.”

So much so that the weevils and larvae actually starved to death rather than feed on other
plants.

In field tests in New Jersey and Delaware, the weevils have decimated mile-a-minute
weed. Some researchers say it’s the most impressive biocontrol they’ve worked with.

For The Environment Report, I’m Sabri Ben-Achour.

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Bugs Released to Munch on Invasive Plant

  • Purple loosestrife's looks are deceiving. It's a beautiful plant, but researchers say it has caused enormous damage in many parts of the country. An imported beetle has now shown significant signs of controlling the plant.

Purple loosestrife is a beautiful plant. It’s tall… and each cone-shaped stem produces hundreds of flowers. When the plants bloom in mid-summer they can create a sea of purple in wetlands throughout the region, but the ability of the plant to spread and reproduce in great numbers is what concerns scientists and land managers. Over the years they have been working to control it. The Great Lakes Radio Consortium’s Mark Brush says one way they’re trying to control it is by releasing a bug to eat the plant:

Transcript

Purple Loosestrife is a beautiful plant. It’s tall… and each cone-shaped
stem produces hundreds of flowers. When the plants bloom
in mid-summer they can create a sea of purple in wetlands
throughout the region… but the ability of the plant to spread and
reproduce in great numbers is what concerns scientists and land
managers. Over the years, they have been working to control it.
The Great Lakes Radio Consortium’s Mark Brush says one way
they’re trying to control it is by releasing a bug to eat the plant:


Roger Sutherland has lived next to this wetland for more than 35
years.

He helped build a boardwalk over the soggy marsh so that he can
get a close-up view of some of his favorite plants:


“You see that plant with the big green flower? Yep. That… and
there’s more along here… that’s a pitcher plant. These are insect
eating plants and there’s another one called sundew here… here’s
some right in here…”

(sound under)


But like many wetlands throughout the country, this wetland has
been invaded by a plant originally found in Europe and Asia.


Purple Loosestrife was introduced as an ornamental plant.
It was a
beautiful addition to gardens, but once it took
hold in the environment,
it out-competed native plants.

Frogs, birds, and insects have relied on these native plants for
thousands of years. Purple Loosestrife is crowding out their habitat.


“We’re going to get a lot more shade with this loosestrife.. and so
these plants that are on these hummocks here…
these little insect
eating plants and so on… just can’t tolerate that shade, so we’ll
probably lose ’em unless I can keep it open here… and I am trying
to keep some of it open.”


The plant spreads quickly… that’s because one plant can produce
more than two million seeds that spread with the wind, like dust.

So when it moves into an area, it often takes over creating a thicket
of purple with a dense root system.

Land managers have seen populations of ducks, and turtles
disappear when loosestrife takes over…

And research has shown that the plant can reduce some frog and
salamander populations by as much as half.


So land managers wondered what to do to stop the spread of this
weed.

They initially tried to control the plant by digging it up… or by
applying herbicide to each plant.

Trying to kill the plants one by one is hard work… especially
considering how abundant purple loosestrife is.

But researchers have hope because of a bug.


(Sound of volunteers planting loosestrife)

Volunteers have gathered here in Ann Arbor, Michigan to plant
purple loosestrife.

They’re putting dormant loosestrife roots into potting containers and
adding fertilizer.


(more sound)


When the plants leaf out they’ll be covered with a fine mesh net and
become home to a leaf-eating beetle known as galerucella.

And galerucella loves to munch on purple loosestrife.

The volunteers are creating a nursery to raise more beetles.

Once they’ve got a bunch of beetles growing on the plant… they’ll
take it to a nearby wetland… and the bugs will be released into the
wild…


(sound up)


Linda Coughenour is a member of the Audubon Society.

Her group is working with state and local agencies to raise and
release these beetles.

She says tackling purple loosestrife invasions is a big task – and
governments need help from volunteers to deal with the problem:


“This is a serious problem throughout the entire Great Lakes
wetlands… it has migrated from the East Coast to the Midwest…
so, uh.. the problem’s just too big – so they thought up doing this
volunteer project and they’ve enlisted people all over the state… and
we’re just one of those.”


Volunteers have have been releasing their beetles into this wetland
for few years now and they’re beginning to see progress:


“It’s going really well… for a while we got off to a slow start, but for two
years now we’ve found evidence that the beetles are reproducing on their
own. We see little egg masses, we see larva that are starting to eat
the plants, we see adult beetles on the plants that have wintered
over. And that’s the thing, to get them to do it on their own.”


But releasing a foreign species into the wild is always a concern.

There are a number of examples of bugs released into the wild to
eliminate a pest, but ended up causing a problem themselves.

But before importing a bug that will prey on plants – the federal
government requires testing to make sure it won’t eat other plants.


The tests have been done.


And researchers feel that this is an extremely finicky bug…


Berndt Blossey is a specialist on invasive plants and ways to control
them.

He says the beetles were tested on native plants before they were
allowed to import the bugs:


“And it was shown there that they will not be able to feed and
develop on the plants. They will occasionally nibble on them, but
they will not be able to develop on them and they usually move off
after they have taken a bite, and they move off to other plants.”


The leaf beetle is not the only bug researchers are importing.

They’re also importing two other beetles known as “weevils.”

One that feeds on loosestrife flowers, and one that feeds on its root
system.

Blossey says more than one bug is needed to keep the plant from
growing back:


“Loosestrife will rebound from resources in the root stock. If you
have the root feeder in the system as well, these fluctuations will be
dampened, so loosestrife will not be allowed to comeback to higher
levels.”


(sound of wetland up)


People who admire the diversity of plants and animals in wetlands
like the idea of keeping purple loosestrife in check.


Roger Sutherland welcomes the bugs.

He believes they’ll help him keep this wetland open for the plants,
birds, and insects he’s come to know over the years:


“We know that the purple loosestrife will probably always be here.
But if we can bring it down to a manageable level, where you’re going
to have a pocket here and a pocket there… and you can kind of
maintain the integrity of this wetland system… then you can’t ask for
anything more than that.”


And researchers say that’s the goal.

To help these wetlands reach a balance… so that plants and animals
that have evolved to rely on these wetlands for thousands of years…
can continue to do so.

For the Great Lakes Radio Consortium, I’m Mark Brush.

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