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Prepare to be Invaded!, or
A Quick Study on Invasive
Organisms
What does it mean to be “invasive”?
1) Exotic (not endemic, or native to
an area)
But that is simply not enough…
2) Able to survive and reproduce
in the new area.
-a distinct breeding population,
more than just a few random
individuals
But this is STILL not enough!
3) The population needs to take over
another populations niche, or force
it out.
-Invasives often become a monoculture, and wreck the ecosystem.
-Loss of diversity, loss of habitat,
loss of food for other organisms, etc..
Things most invasive species
have in common:
1) No natural predators, so nothing to
hold the population down.
2) Usually very prolific, reproducing
very rapidly.
3) Have characteristics that exclude
native species from a habitat.
Some Quick Numbers:
$137 BILLION dollars in damage
due to invasives every year.
50,000 exotic species (estimated)
are released in the US every year.
But there is some GOOD news!
The 10% Rule
Only 10% of introduced exotics will
live at all.
-Wrong climate, food availability, etc..
Of the 10% that live, only 10% will
actually be able to breed and become
invasive.
-You need to find a mate and the proper
conditions to raise young.
Invasive Organisms in Delaware
-There are a number of invasive, nonnative organisms that have made
Delaware their home. Below is a
sample of some of the most invasive,
some of which you might think are
native organisms.
1) Kudzu vine
-Native of Asia, brought to the U.S. to
control erosion along river banks and
new ditches
-infests 2-3 million acres in eastern
U.S., with an annual loss of over $50
million due to lost productivity, and
cost of control.
2) Nutria:
-small wetland mammal, brought from
South America for its fur. The fur
trade never really took off, now it’s a
very bad pest in wetlands.
-it eats young shoots and roots, killing
marsh plants, destroying wetlands
3) Multiflora Rose:
-Native to Asia, brought to U.S. from
Japan in the 1800’s.
-Used to control erosion along rivers
and act as a “living fence”.
-Forms dense thickets, crowds out
native plants and animals.
-Very prolific breeder, makes many
seeds, can grow just about anywhere.
4) Gypsy Moth:
-introduced to this country from Asia
in 1868, accidentally.
-voracious eaters, especially fond of
oak trees.
-is responsible for the general decline
in numbers of oaks in forests over the
past 100 years.
5) Purple Loosetrife:
-Native to Europe/Asia
-Introduced in the 1800’s to U.S.
-wetland plant, very aggressive
competitor for land, nutrients.
-crowds out native reeds, cattails.
-extremely prolific, one plant can
produce over 30,000 seeds.
6) Honeysuckle:
-Imported from Japan in 1862 to Long
Island, N.Y.
-Very tenacious vine, covers and pulls
down large trees and shrubs
-Often grows in disturbed areas, such
as roadsides, and along edges of forests.
7) European Green Crab
-Native to Africa/Europe
-tolerates a wide variety of conditions
-eats many more clams/mussels than
native crabs, causing a decrease in
numbers of clams.
-pushes many other crabs out of the
habitat, and takes over (aggressive).
NATIVE
Calico Crab
INVASIVE
European Green Crab
8) Mute Swan:
-Native to Europe
-introduced to U.S. by European
admirers, has shown a great population
increase since introduction.
-very aggressive, competes with native
waterfowl for food and breeding space.
-is taking over in many places.
9) European Starling
Introduced in 1890 as part of a plan to
introduce to the U.S. all birds mentioned in
the works of Shakespeare. (12 birds released)
Very aggressive, pushes native song birds away
From feeders and nesting areas.
Highly prolific, they breed in conditions that other
birds cannot, and so have a high population.
(Estimated at over 200 million in the U.S.)
10) Japanese Beetles
Introduced accidentally into New Jersey from
Japan in 1916 and is now widespread over the
eastern United States.
Both the grub and the adult are voracious eaters,
and cause widespread damage to trees, shrubs,
and grass.
Introduction of Invasive Species
1) Intentional Introduction
-for economic purposes (Ex: nutria)
-for cultural purposes (Ex: starlings, Asian
Shore crabs)
-for aesthetic reasons (Honeysuckle, Purple
Loosestrife
-for misguided environmental projects (Kudzu,
Multiflora rose)
2) Accidental Release
-Ballast water transfer from foreign areas
(Green crab, Zebra Mussel, Comb Jellyfish)
-Accidental release of organisms (gypsy moth,
“Killer” African bees
-Transfer in packing material (European Green
Crab to California, Horned Asian Beetle)
Control of Invasives
Much of the control of invasive pests
relies on the ability to lower the
population early on, before the size
has grown beyond our capability
to handle it.
-Once the population has a “foothold”, it
is much harder, if not impossible to
eliminate.
Control vs. Eradication
It may not always be in our best
interests to completely eliminate a
population of pests.
-economics and environmental damage
play a role in deciding to eradicate an
invasive.
-Is the cure better than the problem?
Past a certain point, eradication will
be virtually impossible in any case.
Usually, by the time the pest is noticed,
the ability to eradicate it has been lost.
-Especially in marine ecosystems, because
of the ability of the organism to go without
being noticed until large numbers exist.
This makes a good case for close
monitoring of critical habitat.
Control of Invasives
Population Size
2500
2000
1500
1000
500
Time (months)
Point of First Discovery
Ability to Control is lost
19
17
15
13
11
9
7
5
3
1
0
Success of control depends on a few key factors:
1) Catching the infestation EARLY, before
population numbers get out of hand.
2) Whether or not the invasive organism is mobile
within the environment.
3) How rapidly the invasive can reproduce.
-does it reproduce in more than one way?
-does it need certain conditions?
4) How vulnerable the invasive is to control.
-is it tolerant to pesticides?
-will it re-grow if burned?
Control Methods
Control Methods can include:
1) No action. This alternative may be chosen if
the pest numbers are low enough that they don't
interfere with management goals
2) Physical (manual & mechanical) management
3) Cultural management
4) Biological management
5) Chemical management
Mechanical or Physical Management:
Mechanical or physical control methods involve
using barriers, traps, or physical removal to
prevent or reduce pest problems.
Tactics may include baited or pheromone
traps to capture insects, or cultivation or
mowing for weed control.
Cultural management: Cultural practices
are a manipulation of the habitat environment
to increase pest mortality or reduce rates of
pest increase and damage.
There are many different cultural practices that
can help to reduce pest impact such as
selection of pest resistant varieties of crops,
mulching, addition of beneficial insect habitat,
or other habitat alterations.
Biological Management: Biological control
is the deliberate use of the pest's natural
enemies - predators, parasites, and
pathogens - to reduce the pest population
below damage levels.
Purple Loosestrife: A Study in Biological Control
Purple loosestrife is a difficult plant to kill with
conventional weed killers because it grows near
bodies of water.
Week killers used on the invasive plants could end
up in the waterways, and cause more damage
to fragile aquatic organisms.
Scientists went back to the origin of the plant and
looked for insects that ate ONLY loosestrife.
Three beetle species have been grown and
released in parts of the U.S. since 1994. Two
of these species feed as both adults and
immature larvae on the leaves and growing
tips. The most promising beetle is Galerucella
calmariensis.
They have one generation per year and
overwinter as adults. Eggs are laid in clusters of
5-20 on the leaf surface, often where the leaf
joins the stem.
Also, larvae feed in the growing tips, which can
reduce or prevent flowering -- and no flowers
means no seeds.
The feeding causes holes in the leaves,
reducing the amount of leaf area, weakening
the plant.
Before the insects were allowed into the U.S.
in the early 1990s, they were tested against
49 species of plants to determine on which
ones what they would feed.
When they were given a simultaneous choice
of purple loosestrife or the native species, the
beetles fed very little on the two native
species, but did NOT lay eggs on them -meaning there would be no damage from
larval feeding and no new generation of
beetles on these species of plants.
There are no guarantees of success, but there
are several beginning signs of promise. At one
site near Savanna, Illinois, (on the Mississippi
River), a total of 1,000 Galerucella beetles
were released at three discrete places in 1994.
In the summer of 1997, there was severe
damage to the loosestrife -- many hundreds of
dead plants, many thousands more that did
not flower, even though other loosestrife in
nearby areas was flowering.
From the release of a few hundred Galerucella
in 1994, flowering at the site was reduced, by
1997, to only 3% of the plants sampled -- a
number small enough that native plants can
return to the area.
Chemical Control: Use of pesticides in a
way that complements rather than hinders
other elements in the strategy and which
also limits negative environmental effects.
It is important to understand the life cycle of a
pest so that the pesticide can be applied when
the pest is at its most vulnerable – the aim is
to achieve maximum effect at minimum
levels of pesticide.
Broad Spectrum vs. Targeted Pesticides
A broad spectrum pesticide kills ALL of the
related pests.
This generally bad because beneficial plants and
animals are killed as well.
A targeted or NARROW SPECTRUM pesticide is
much better for the environment because the
beneficial organisms are not harmed.
A Brief Story of Some Invasives
The St. Lawrence Seaway is the common name for a
system of canals that permits ocean-going vessels to
travel from the Atlantic Ocean to the North American
Great Lakes, as far as Lake Superior.
The Seaway opened in 1959 and
cost $470 million US dollars.
The creation of the seaway also led to the introduction
of foreign species of aquatic animals, including the
sea lamprey, alewife, and the zebra mussel, into the
Great Lakes Basin.
These organisms were introduced via ballast water
from oceanic vessels.
Common Alewife