Watch Out Water-hyacinth!
New Jungle Enemies Are Coming
Above, grey-white nymphs of Taosa
plant hoppers feed on heavily damaged
water-hyacinth. The sap-sucking insects not
only damage and weaken the weed,
they introduce plant pathogens.
You can't get to Iquitos, Peru,
without a boat or a plane. But this jungle-locked city of 350,000 in the
rainforests of the upper Amazon River is the business and tourism hub of Peru's
In the late 19th century, rubber made Iquitos a major trade center. Today,
tourists can visit old rubber-baron mansions like Casa de Hierro (Iron
House), designed by Gustave Eiffel of Paris.
Iquitos has a different appeal for Agricultural Research Service entomologist
Hugo Cordo. "This region may be the world's richest source of natural
enemies of water-hyacinth," he says. Cordo leads the ARS South American
Biological Control Laboratory in Buenos Aires, Argentina. Water-hyacinth,
Eichhornia crassipes, is a free-floating perennial herb. The plants grow
about 3 feet tall as they float on the water's surface, with stems intertwining
to form dense mats.
In the Amazon the plant is held in check by natural enemies such as insects
and microbes. These organisms stress the plants, controlling the mat's
expansion. But water-hyacinth has escaped to friendlier waters, especially
since the 1800s. Often, visitors, drawn by its lush leaves and blue-to-lavender
flowers, have taken it home as an ornamental.
Petioles of water-hyacinth densely
punctured by oviposition marks
of Taosa plant hoppers.
A Floating Nightmare
Out of its enemies' reach, water-hyacinth has become the worst floating
aquatic weed in many tropical and subtropical parts of the Americas, Asia,
Australia, and Africa. In Africa it infests every major river and nearly every
major freshwater lake. In the United States, it flourishes in hundreds of
bodies of water in Hawaii and California and throughout the South from Texas to
Today, increased cooperation by governments and scientists around the world
is turning up the heat on water-hyacinth. The more unique natural enemies that
scientists can find and evaluate, the more likely they can deploy new
biological control cadres suited to the weed's various growth stages and to
different climates and other conditions.
At worst, this plant may be a killer. In the Sepik area of Papua New Guinea,
it has been blamed for making people starve. According to Australian scientists
K.L.S. Harley, M.H. Julien, and A.D. Wright, people "could not access
subsistence gardens, hunting areas, catch fish, or travel to market to sell and
buy produce" because of dense water-hyacinth mats.
More typically, water-hyacinth damages water quality by blocking sunlight
and oxygen and slowing the water's flow. Capable of doubling within a couple of
weeks, it can grow faster than any other plant. By choking out other
vegetation, it makes an area unusable by plants and animals that live in or
depend on the water. Fish spawning areas may vanish.
The Megamelus plant hopper (about 3mm
long) may provide badly needed help in controlling water-hyacinth.
In the Florida Everglades of the
United States, the snail kite (Rostrhamus sociabilis) is endangered
partly because this bird can't find apple snailsits favorite
foodwhere the weed has smothered the snail's favored food plants. In some
parts of the world, the mats form habitat for disease-carrying mosquitoes as
well as snail species that are intermediate hosts for schistosomiasis, among
the world's worst parasitic diseases.
Uncontrolled, water-hyacinth robs water from potential drinking and
irrigation supplies. The mats can block boat travel. Chunks of mat can break
free to clog downstream pump stations supplying water for drinking, irrigation,
Chemicals and mechanical removal, the primary weapons against the weed, are
costly and often ineffective.
Searching for Its Nemesis
Scientists believe that the best bet for a long-term solution is to
introduce one or more natural enemies as biological controls.
Two decades ago, Cordo and ARS entomologist Jack DeLoach in Temple, Texas,
led an effective biological control program at Argentina's Dique los Sauces
reservoir. In the 1970s, ARS researchers Ted Center and Neal Spencer were the
first to release in the United States two South American weevils (Neochetina
bruchi and N. eichhorniae) and the water-hyacinth borer (Sameodes
These and other organisms are being deployed in more than 20 other
countries, including Australia, Cuba, Egypt, Honduras, Indonesia, Malaysia,
Mexico, Panama, South Africa, Thailand, Vietnam, and Zimbabwe. There have been
many successes, but results have been variable and the weed continues to cause
The natural beauty of water-hyacinth's
flower and foliage has helped it
spread to become a floating
nightmare in many tropical areas.
"For years," says Cordo,
"we thought most of the best potential biological control agents were
"But until now," Center notes, "no one had really looked for
them in the upper Amazon. That is probably the area where water-hyacinth
originatedwhere you might expect to find the greatest diversity of
natural enemies." Center leads ARS' Aquatic Plant Control Research Unit in
Fort Lauderdale, Florida.
This scientific optimism brought Cordo, Center, and three other scientists
to Iquitos in late April 1999. The others were entomologist Martin Hill with
South Africa's Plant Protection Research Institute and plant pathologists Harry
Evans and Djami Djeddour of CABI Bioscience in England.
They searched for natural enemies along 180 kilometers of the upper Amazon
and the two rivers that converge to form itthe Ucayali and
Into the Thick of It
On April 27, guide Andrés Guerra motored the group down the Amazon in
a small aluminum boat. "We were looking for water-hyacinth growing in
cochas," Cordo says. Cochasbayous and depressions away
from the river channelare typically concealed behind the wall of
rainforest lining a river channel.
Thrypticus fly (about 2 mm long).
Eventually the group stopped at an
area Guerra said was near cochas. With a machete, he hacked low branches
and vines to clear the boat's path through the flooded forest. "For a half
hour," says Cordo, "we thought we were heading to nothing. But
suddenly, the cochas were there. We steered into the water-hyacinth mat
and began using our hands and a sweep net to collect insect and plant
In all, the scientists collected hundreds of natural enemies and plant
samples at 30 sites in 7 days. From the first day, the excitement was about a
tiny insect, a water-hyacinth fly that none of the scientists had seen before.
In Buenos Aires, Cordo's team had already been testing several promising
insects, including three species of Thrypticus flies collected since
1996 in Argentina. Now, it appeared they had found a new Thrypticus.
Water-hyacinth in bloom.
The female Thrypticus
deposits an egg in a water-hyacinth petiolethe stalk that attaches the
leaf to the stem. The young larva feeds on the inner tissue. Within the petiole
it digs ultranarrow tubes called mines. The mines have one or more tiny spurs
that exit the petiole's outer skin. "Water doesn't enter these tiny
orifices," Cordo says, "and we don't know why the fly makes them. But
they may serve as doorways for pathogens to enter and further weaken the
Each Thrypticus species has a unique mining pattern. One is shaped
like the letter "U"; another is C-shaped. But at site 1and
later, other sitesthe scientists found ringlike mines with several
orifices. "We believe the Thrypticus that made these is a new
species," Cordo says. "And it appears to be a specialist in attacking
very young petioles."
A Bountiful Harvest
During the trip, the scientists also found as many as three new species of
Taosa plant hoppers. Only one had been reported in the scientific
literature. Taosa and Megamelus plant hoppers are sap-sucking
insects that, like their whitefly cousins, can transmit plant pathogens. Cordo
says the Taosa especially "are impressive because of their impact
in combination with a pathogen we have not yet identified. Infested plants were
short, weak, and full of spots made by the pathogen."
The insect identifications are preliminary, but 11 species new to science
have been collected so far by the ARS research team on water-hyacinth and its
relatives in Iquitos and northern Argentina since 1996: six Thrypticus,
three Taosa, and two Megamelus species.
The ARS scientists at Buenos Aires have been conducting numerous studies of
the insects' biology and behavior. They will screen colonies of insects they
collect to find out which might do the most damage to water-hyacinth.
They are also making sure water-hyacinth is the only important plant
attacked. "Along with crops, this means testing ornamentals and plants in
natural settings," Cordo says. "We've already determined that the new
Thrypticus and one of the Megamelus do not attack plants in other
families. And they will not attack the one U.S. plant in the water-hyacinth
family that we don't want to hurt." That plant, pickerel weed, is used by
many small aquatic animals.
Cordo, Center, and Hill, the South African scientist, are collaborating to
determine how best to rear Megamelus and Thrypticus for lab and
outdoor tests. "With luck," Cordo says, "Thrypticus might
be ready to import in 2 or 3 years, for testing first in the Fort Lauderdale
lab. With Megamelus, that time may come sooner, since we already know
how to rear small lab colonies of it."By
Jim De Quattro, ARS.
This research is part of Crop Protection and Quarantine, an ARS National
Program (#304) described on the World Wide Web at
Hugo Cordo is at the
USDA-ARS South American
Biological Control Laboratory, Hurlingham, Argentina; telephone and fax
54-11-4662-0999 . His mailing address is Agricultural Counselor, ARS Lab, U.S.
Embassy Buenos Aires, Unit 4325, APO AA 34034-0001.
Ted D. Center is at the
Aquatic Plant Control Research Unit, 3205 College Ave., Fort Lauderdale, FL
33314; phone (954) 475-0541, ext. 103, fax 954-476-9169.
"Watch Out Water-hyacinth! New Jungle Enemies Are
Coming" was published in the March
2000 issue of Agricultural Research magazine.