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Issue date: Jan-Feb 2002
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Science briefs
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 Nonnative Argentine ant workers nurture scale insects in exchange for the sweet honeydew they excrete. By protecting scale, aphids and other homoptera from potential predators, Argentine ants promote populations increases among these agricultural pests. Photo by Marc Dantzker |
By replacing native ants, the tiny black Argentine ant a well-known
household pest could be disrupting natural ecosystems. A study by
UC Davis graduate student Caroline Christian, published in Nature
(October 2001), has shown that when key beneficial species are
removed by an invading ant, the destructive effects can reverberate
through the ecosystem.
Christian,
who is affiliated with the UC Davis Center for Population Biology,
studied the fynbos shrublands of South Africa, an area similar in
climate and vegetation to the chaparral of California. Wildfires
sweep the fynbos every 15 to 30 years, killing most mature plants;
new plants grow from seeds buried in the ground by native ants.
Christian found that when Argentine ants displace native ants, plants
that depend on those ants to bury their seeds do not regenerate
after fire.
Seed burial
by ants is key to survival for about a third of fynbos plant species,
Christian said. When fresh seeds fall, ants are attracted to them
and carry them off to bury in their nests. Different ant species
specialize in seeds of different sizes: Ants that work cooperatively
deal with bigger seeds, while ants that tend to work alone bury
smaller ones. If the seeds are not picked up quickly, virtually
all are eaten by rodents.
After controlled
burning, fynbos areas invaded by Argentine ants showed a tenfold
drop in the number of new plants from large-seeded species, compared
to uninvaded areas, Christian said. Small-seeded species were much
less affected.
California a supercolony of Argentine ants
In a study published in Molecular Ecology (September 2001),
scientists from UC Davis and UC San Diego showed that California
harbors a huge supercolony of nonnative Argentine ants, extending
from Ukiah to beyond the Mexican border.
In Argentina,
competition between rival colonies keeps their numbers in check,
but most of the California imports recognize each other as family,
said Neil Tsutsui, a postdoctoral fellow in the UC Davis Center
for Population Biology.
"In
ants, usually their biggest competition is within the same species.
But here, colonies are so closely related they even exchange workers,"
said collaborator Andy Suarez, a former UC Davis entomology postdoctoral
fellow now at UC Berkeley.
Because they
were initiated by a relatively small number of individuals, introduced
populations of Argentine ants have reduced genetic diversity and
are genetically similar to one another, the scientists found. This
close-knit sisterhood allows Argentine ants to form large supercolonies,
which then displace native ants and become one of California's leading
household and agricultural pests.
Tsutsui and
Suarez, working with David Holway and Ted Case at UC San Diego,
used a type of DNA fingerprinting to show that Argentine ants in
California are genetically similar to ants along the southern Parana
River in Argentina. Efforts to identify natural enemies of the Argentine
ant for biological control should focus on this area, Tsutsui said.
Earlier research
by Suarez and the same colleagues traced the rapid decline of coast
horned lizards in California to indirect impacts of invading Argentine
ants. The invaders displaced indigenous ants, the lizard's favored
food source. They are not a palatable substitute.
In related
research published in several journals, the four scientists also
showed that the loss of genetic diversity in introduced populations
led to reduced aggression among the ants, allowing the formation
of the supercolony in which queens and workers mix freely among
separate nests. The invaders wipe out indigenous ants through sheer
numbers.
SOD found on UC Berkeley campus
A pathogen that has devastated wide swaths of California's oak
trees has been discovered on the grounds of UC Berkeley, campus
officials announced Oct. 31, 2001. The microbe responsible for sudden
oak death (SOD) has infected three host species, including two California
bay trees near the Faculty Glade. The infection has not been detected
in any of the oak trees on campus, suggesting that it arrived recently.
Matteo Garbelotto
of the UC Berkeley College of Natural Resources noticed the infections
while walking through campus. Subsequent tests confirmed that the
infections were caused by Phytophthora ramorum (see California
Agriculture, January-February 2001). Garbelotto and UC Davis
associate professor Dave Rizzo, in conjunction with the California
Oak Mortality Task Force, were recently awarded a $1 million grant
from the San Francisco-based Gordon and Betty Moore Foundation,
to study P. ramorum.
Approximately
50 campus groundskeepers, gardeners, arborists and horticulturists
from UC Berkeley's Botanical Garden have received training to identify
signs of SOD infection. They are canvassing the campus and gathering
samples of suspicious vegetation. Disease management will include
regular monitoring of the campus grounds and preventative treatments
with fungicides. Areas surrounding the campus also will be surveyed
through a joint effort between UC Berkeley and the Alameda County
Agricultural Commission.
There are
at least 10 known tree and plant species that are susceptible to
the P. ramorum pathogen. The highly contagious microbe is
a brown algae related to the species responsible for Ireland's potato
famine of the mid-1800s. Its ability to infect a wide array of plant
life through soil, water and air has made it particularly difficult
to control.
SOD was first
noticed in Marin County in 1995 and has since felled tens of thousands
of coast live oaks, black oaks and tan oaks in the state. Infections
have recently been discovered along Crow Canyon Road in Alameda
County and near Lake Madigan in Solano County.
Mondavi gift benefits UC Davis wine and food sciences
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 A $25 million gift from Robert and Margrit Mondavi will allow UC Davis to build a new facility combining viticulture, enology, and food science and technology. Graduate student Fiona Hutchinson pours peanuts into a machine that coats them with an edible covering made from whey proteins, a byproduct of cheese processing. The coating prolongs freshness while utilizing a dairy byproduct that has long been a waste disposal headache for cheese processors.. Photo by Tony Novelozo/Axiom |
On Sept. 19, 2001, Robert and Margrit Mondavi announced
a personal gift of $25 million to UC Davis to establish the Robert
Mondavi Institute for Wine and Food Science. The gift will be combined
with campus funds and other private contributions to create new
state-of-the-art research and teaching facilities, to house the
UC Davis College of Agriculture and Natural Resources departments
of viticulture, enology, and food science and technology.
The institute
will include an academic building of approximately 75,000 square
feet for classrooms, laboratories, offices and meeting rooms. A
13,000-square-foot plant for food-processing, and a 36,000-square-foot
building for a new campus teaching and research winery, also will
be constructed within the proposed institute. Current plans call
for the institute to be located on Old Davis Road; ground- breaking
is expected in 2004.
The gift
is the largest private contribution ever to UC Davis and represents
one of the most generous single gifts from an individual donor in
UC history. The Mondavis also donated $10 million to name the UC
Davis campus's Center for the Performing Arts, which is currently
under construction.
— Compiled from U.C. and other news sources
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