The scientists took native gray treefrog tadpoles from
ponds at Patuxent, placed them in aquarium tanks, and exposed them to
doses of the three pesticides common in rain runoff at the edge of farm
fields in the mid-Atlantic Coastal Plain area during the growing season.
They also set up 12 outdoor ponds at Patuxent.
"We saw a pattern of exposure that was similar to
what we've seen in actual wetlandshigh initial exposures caused
by spring rains right after herbicides and insecticides are applied,"
The study showed that a combination of three commonly
used pesticidesatrazine, metolachlor, and chlorpyrifoscould
play a role in frog disappearance. While those pesticides break down
faster in outdoor ponds than in lab aquarium tanks, there are cases
where exposure can persist for extended periods and tadpoles may be
Blowing in the Wind
An earlier paper, published in Environmental Toxicology and Chemistry
in 2001, concerned pesticides and amphibian population declines in California.
Laura McConnell, an ARS chemist and EQL authority on the atmospheric
deposition of pesticides, did the study with Sparling and Gary M. Fellers,
who is with the U.S. Geological Survey's Western Ecological Research
Center at Point Reyes, California.
They investigated the possibility that wind-blown pesticidesparticularly
organophosphate insecticideshave a role in the drastic decline
of toads and frogs over the past two decades in the Sierra Nevada Mountains
downwind of the intensely agricultural San Joaquin Valley. McConnell
says that, "We didn't prove that pesticides cause this decline,
just that it is a possibility. But we did demonstrate that the concentrations
and frequency of pesticide detections in amphibian tissue follow north-south
and west-east patterns consistent with intensified agriculture upwind
of the areas with the most serious amphibian declines. And we showed
that the pesticides are present in the frog tissue and that the frogs
have been exposed to pesticides."
Pacific treefrog tadpoles and adults were sent to the EQL for analysis
for the presence of pesticides in their tissue. They were also sent
to Patuxent to measure levels of an enzyme that indicates exposure to
organophosphate insecticides. More than half of the tadpoles and adults
from Yosemite National Park in California's Sierra Nevadadownwind
of the agricultural areacontained measurable levels of these chemicals,
compared with only 9 percent at the coast.
The evidence from that study added to a growing body of evidence from
other published studies that wind-blown pesticides from Central Valley
farms may have played a role in the decline of amphibians in the Sierra
The results of the Sierra Nevada study also matched observations by
ARS, NRCS, and Patuxent scientists, both from the Patuxent study and
when they visited farm ponds on Maryland's Eastern Shore. For example,
at one of the experimental outdoor ponds at Patuxent, they saw complete
mortality of frogs, crayfish, fish, and other aquatic life, seemingly
caused by a combination of chlorpyrifos, an organophosphate insecticide,
with the herbicides atrazine and metolachlor. Drifts of these sprays
are common during the growing season. This, and other studies conducted
by EQL scientists and others, indicate that pesticide drift might play
a role in the disappearance of frogs worldwide, although it doesn't
appear to cause frog deformities. It may be that if pesticides have
any harmful effect, it is only in combination with other stresses, such
as increased ultraviolet rays, attack from fungi, and infections.
GYPCHEK, World's First Virus-Based Biopesticide
Insect pests of agricultural importance can also be important to wildlife
researchers. The gypsy moth demonstrates both that connection and the
value of native fauna and flora to researchers.
For example, the trees at BARC and surrounding properties gave ARS
scientists at the Insect Biocontrol Laboratory (IBL) the chance to help
turn a natural virus into one of the first virus-based biopesticides.
Called GYPCHEK, the biopesticide has proven effective over years of
ARS research in controlling gypsy moths. The only reason it has not
gone into commercial production has been the lack of a company willing
to manufacture and market it.
ARS entomologist Kevin Thorpe and his IBL colleagues, working with
USDA's Forest Service and Animal and Plant Health Inspection Service,
hope to change that by lowering the costs of mass-producing the virus.
They are seeking a way to grow the virus in a lab, instead of in live
gypsy moth caterpillars. The mass-rearing of caterpillars adds too much
to the production costs, making it less viable commercially.
GYPCHEK was recently used to treat 1,000 acres at BARC, along with
3,024 more acres owned by Patuxent, NASA's Goddard Space Flight Center,
and three other federal agencies. This was the first operational use
of GYPCHEK on the "Green Wedge," a mass of heavily forested
land owned by BARC, Patuxent, and other government agencies in the Washington,
D.C., suburbs. It was one of the largest operational uses of GYPCHEK
made to date.
Thorpe not only researches gypsy moths, he also runs a program to control
them at BARC. In 1988, a couple of years before his arrival, the moving
gypsy moth "front" reached BARC unexpectedly, causing defoliation
that hurt birds and wildlife. It also had the potential to cause "forest
fragmentation" as has happened in many places in the Northeastoften
because of gypsy moth invasion. BARC countered with a control program
that has prevented significant additional damage from occurring.
For this control program, Thorpe and colleagues count egg masses and
use those counts to decide when to spray.
Coexisting With a Multitude of Species
Thorpe heads the BARC Ecology Committee, which was founded in 1977
by Paul Putnam, then BARC director, to protect the fauna and flora of
the forested Green Wedge while farming and researching at BARC.
Many forest-dwelling birds live on the Green Wedge, including neotropical
birds that migrate from South to North America each year to breed or
stay for the winter. The area is home to a variety of other birds, including
nesting bald eagles, hawks, owls, bluebirds and several other songbirds,
wild turkeys, herons, and waterfowl. Many species of warblers sensitive
to forest fragmentation live there, too, along with beavers, muskrats,
deer, foxes, raccoons, opossums, groundhogs, and other four-legged animals.
Several uncommon fish species occur in the streams. Frogs, salamanders,
snakes, turtles, lizards and other amphibians and reptilesplus
diverse insectsare among the Green Wedge's wild inhabitants.
Biodiversity Meets Sustainable Agriculture at BARC
The first step in protecting fauna and flora is to document exactly
what you have.
So that's just what Edward Terrell, a retired BARC botanist, did. He
led a team that recently finished an inventory of the flora of BARC.
Joseph H. Kirkbride, a botanist with the ARS Systematic Botany and Mycology
Laboratory (SBML), has modified this list, which includes two rare species
of orchids. His updated edition, due this summer, will include 4 more
species, for a total of 905 plant species, 141 of them rare and another
12 rare to infrequent. The list is being linked to online plant photo
sites and other databases so it can serve as a plant identification
guide as well as a list. It will soon be accessible from the lab's home
page at http://nt.ars-grin.gov.
These inventoried plants include invasive weeds of national interest,
as well as desirable native plants growing in wildflower and other natural
meadows at BARC. Since you have to know your enemy to vanquish it, BARC
even employs a "weed librarian," Ruth Mangum, to make sure
that sufficient quantities of pest plants are available for researchers
The natural meadows are part of a sustainable agriculture demonstration
project on BARC lands. More than a decade ago, the farm began using
sustainable agricultural practices developed through ARS research. This
has resulted in a lowering of pesticide use by 75 percent. In this way,
BARC has for a long time now been practicing the "farm without
harm" philosophy that ARS has preached for many years. And thisalong
with the continuing research collaboration of two different, committed
federal agencieshas led to a healthy coexistence of diverse plant
and animal life in this outdoors laboratory.By Don
Comis, Agricultural Research Service Information Staff.
This research is part of Water Quality and Management (#201), Air
Quality (#203), and Crop Protection and Quarantine (#304), three ARS
National Programs described on the World Wide Web at www.nps.ars.usda.gov.
For more information about scientists mentioned in this story, contact
Don Comis, USDA-ARS Information
Staff, 5601 Sunnyside Ave., Room 2218-C, Beltsville, MD 20705-5129;
phone (301) 504-1625, fax (301) 504-1641.
"Farming Without Harming" was published in the October
2003 issue of Agricultural Research magazine.