Fire Ant Outcompetes Other Species—Even in its Native Habitat

By Alfredo Flores
July 2, 2009

Even in its native Argentina, the fire ant wins in head-to-head competition with other ant species more than three-quarters of the time, according to Agricultural Research Service (ARS) scientists.

ARS scientists at the South American Biological Control Laboratory (SABCL) in Hurlingham, Argentina, have been studying how different ant species fare against the fire ant as part of an effort to learn more about the behavior of this pest—an invasive species in its non-native United States.

Fire ants often attack in swarms--not only causing painful stings to humans, but can even kill small animals. Little has been known, however, about the fire ant's competitive nature or how it interacts with other ants.

SABCL biologist Luis Calcaterra, working closely with lab director Juan Briano, has been studying interactions between the red imported fire ant, Solenopsis invicta, and other aboveground foraging ants in two habitats in northeastern Argentina—using a combination of pitfall traps and baits to study day-to-day activity in ant communities.

The pitfall trap is a 50 milliliter plastic tube buried in the ground and half-filled with soapy water. The bait is one gram of canned tuna placed on a plastic card measuring five centimeters in diameter. The trap and bait gave the scientists a way to determine ant populations at the sites, and showed the dominance of each species.

Some 28 ant species coexisted with S. invicta in an open area of forest growing along a watercourse, whereas only 10 species coexisted with S. invicta in the dry forest grassland. The researchers found that the fire ants had the highest numbers in the open forest area along the watercourse.

Prior to these studies, it was thought that the fire ant—now established throughout the Americas—was not dominant in its native land. But the studies showed that the fire ants were the most ecologically dominant, winning 78 percent of the interactions with other ants, mostly against its most frequent competitor, the South American big-headed ant, Pheidole obscurithorax, an ant of northern Argentina and Paraguay also introduced in the United States. And in battles with the invasive Argentine ant, Linepithema humile, the fire ants were even more dominant, winning out 80 percent of the time.

This study was published in Oecologia, a journal that deals with plant and animal ecology.

Read more about the research in the July 2009 issue of Agricultural Research magazine.

ARS is the principal intramural scientific research agency of the U.S. Department of Agriculture.

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ARS scientists have developed a new bait that may help control varroa mites, the top pest of honey bees. Click the image for more information about it.

Finding out how genes govern bees' lives   The latest buzz on Russian bees   New test on tap for detecting pesticide-resistant mites

New Bait Lures Varroa Mite to its Doom

By Jan Suszkiw
July 1, 2009

Varroa mites could literally be walking into a trap—thanks to a new attractant developed by Agricultural Research Service (ARS) scientists in Gainesville, Fla.

The 1/16-inch long parasite, Varroa destructor, is a top pest of honey bees nationwide, hindering the beneficial insects' ability to pollinate almonds, blueberries, apples, zucchini and many other flowering crops.

At the ARS Chemistry Research Unit in Gainesville, research leader Peter Teal and colleagues are testing a bait-and-kill approach using sticky boards and natural chemical attractants called semiochemicals.

In nature, Varroa mites rely on these semiochemicals to locate—and then feed on—the bloodlike hemolymph of both adult honey bees and their brood. Severe infestations can decimate an affected hive within several months—and rob the beekeeper of profits from honey or pollinating services. But in this case, the mites encounter a more heady bouquet of honey bee odors that lure the parasites away from their intended hosts and onto the sticky boards, where they starve.

In preliminary tests, 35 to 50 percent of mites dropped off the bees when exposed to the attractants. Free-roving mites found the semiochemicals even more attractive, according to Teal.

Moreover, the extra dose of semiochemicals wafting through hives didn't appear to significantly interfere with the honey bees' normal behavior or activity, added Teal who, along with postdoctoral associate Adrian Duehl and University of Florida collaborator Mark Carroll, reported the results this past January at the 2009 North American Beekeeping Conference in Reno, Nev.

The team hopes ARS' patenting of the Varroa mite attractants will encourage an industrial partner to develop the technology further.

Read more about the research in the July 2009 issue of Agricultural Research magazine.

ARS is the principal intramural scientific research agency of the U.S. Department of Agriculture.

It may not always pay for ranchers to use herbicides to kill exotic invasive weeds on the range, according to a new study. Click the image for more information about it.

Knowing where to look for invasive leafy spurge   Seeded pastures can sustain cattle-and native rangelands   USDA Livestock and Range Research Lab expansion unveiled

Spraying Herbicide on Invasive Weeds Doesn't Always Pay, Study Shows

By Don Comis
June 30, 2009

It may not always pay for ranchers to use herbicides to kill exotic invasive weeds such as leafy spurge, according to a 16-year study by the Agricultural Research Service (ARS) and colleagues.

Rangeland ecologist Matt Rinella at the ARS Fort Keogh Livestock and Range Research Laboratory in Miles City, MT, and colleagues conducted the study. Data they collected 16 years after a one-time aerial spraying of herbicide showed that the invasive leafy spurge (Euphorbia esula L) may have ultimately increased due to spraying. Conversely, several desirable native forbs were still suffering the effects of spraying 16 years after spraying.

Although the herbicide would have dissipated within a few years, it seemed to cause a long-term plant community shift.

Any increase in grass production from the herbicide spraying only lasted a year or two.

The study was done on the N-Bar Ranch in Montana. Each plot was either grazed and sprayed, grazed but not sprayed, not grazed but sprayed or not grazed or sprayed. Cattle grazing helped maintain native plant numbers when herbicide was used.

Cattle grazing can help native forbs thrive because cattle prefer grasses over forbs, and cattle trample soil, loosening soil for seeds that the animals inadvertently plant when seeds are caught in their hooves or fur. That said, when herbicide wasn't used, most native forbs did as well with or without cattle grazing.

Herbicide caused the native plants Missouri goldenrod and yarrow to become rarer over the 16-year study period. Barring herbicides, these two species proved capable of co-existing indefinitely with the exotics.

Four native perennials became rarer in sprayed plots, but only when grazing was excluded: velvety goldenrod, white prairie aster, vetch, and prairie sagewort. Herbicide spraying caused no long-term harm to four other native perennials. Rockjasmine and other plants belonging to the Androsace spp. group were not affected by the herbicide even initially.

The study suggests that applying herbicides over large areas of land containing herbicide-sensitive native plants is sometimes ill-advised.

The research was published in the journal Ecological Applications.

ARS is the principal intramural scientific research agency in the U.S. Department of Agriculture.

New research is shedding light on how endophytic fungus-infected fescue causes fescue toxicosis--a disease that affects grazing animals and costs the U.S. cattle industry an estimated $600 million annually. Click the image for more information about it.

Food for thought: forage   A forage laboratory for America's Mid-South

Connecting the Dots for Alkaloids, Toxicosis Symptoms

By Laura McGinnis
June 29, 2009

New research from Agricultural Research Service (ARS) scientists and their university colleagues is shedding light on the relationship between chemical compounds and fescue toxicosis—a disease that affects grazing animals and costs the U.S. cattle industry an estimated $600 million annually.

Fescue toxicosis is a major problem for producers whose herds graze on tall fescue. A major forage grass in many states, tall fescue can cause toxicosis in cattle and other ruminants if it's infected with endophytic fungus. The disease causes lameness and reduced production efficiency, and can even be fatal if infected animals are subjected to stressful situations, such as extreme heat or long-distance transport.

Scientists believe many symptoms of toxicosis are caused by chemical compounds known as ergot alkaloids, but much is still unknown about how they cause clinical signs to develop. Led by ARS animal scientist James Klotz, scientists at the ARS Forage Animal Production Research Unit in Lexington, Ky., and the University of Kentucky are investigating the physiological responses of ruminants to tall fescue alkaloids.

One sign of toxicosis is a narrowing of blood vessels. Using a model that predicts changes in blood flow in the limbs of cattle, Klotz and his colleagues examined the influence of specific alkaloids—both individually and in combination.

Of the three alkaloids tested, ergovaline was the most effective at making the veins contract. The others, N-acetylloline and lysergic acid, had little effect on vein contraction. The results also showed that combining two alkaloids did not increase the toxicity of either—at least in terms of vein contraction.

Further research is underway to determine how these alkaloids influence other tissues, organs and physiological systems. In one study, the scientists showed that ergovaline, but not lysergic acid, can bioaccumulate in vitro, suggesting that ergovaline may be more likely to induce toxicosis.

Research like this is essential for understanding exactly how endophyte-infected tall fescue influences grazing animals. Eventually, this information could help scientists determine which compounds are most toxic and how to protect cattle from them.

These studies were published in the Journal of Animal Science.

ARS is the principal intramural scientific research agency for the U.S. Department of Agriculture.

ARS hydraulic engineers are helping the Natural Resources Conservation Service rehabilitate aging small dams across the country by increasing their utility and safety with roller compacted concrete stepped spillways. Photo courtesy of NRCS.

Stronger embankments start in the lab   "Sound" technology used in sediment research   Maintaining the safety of earthen dams

New Designs for Making Old Dams Safer

By Don Comis
June 26, 2009

A group of Agricultural Research Service (ARS) hydraulic engineers are helping to rehabilitate aging small dams across the country.

Efforts are underway to upgrade existing auxiliary spillways or build new spillways for these dams, especially in Oklahoma. These upgraded or new spillways meet current dam safety standards and will increase the useful lives of the dams.

The U.S. Department of Agriculture's Natural Resources Conservation Service (NRCS) has helped build more than 11,000 earthen dams over the years as part of its Watershed Protection and Flood Prevention Operations Program. These dams serve many purposes, but the primary purpose is flood control. Since the program began in 1944, ARS Hydraulic Engineering Research Unit (HERU) engineers in Stillwater, Okla., have partnered with NRCS in the development of design standards for the dams.

When ARS hydraulic engineer Sherry L. Hunt and her colleagues were asked recently by NRCS to help evaluate and design retrofitted Roller Compacted Concrete (RCC) stepped spillways for dams in Georgia and North Dakota, they found the same technology also can help increase flow capacity on many of these dams across the country. So they developed generalized criteria for designs that could be used anywhere in the country.

Compacting concrete with a roller is a fast way to make a tough surface.

With the many changes that have occurred over the years—including deterioration, changes in upstream and downstream land use and population, and changes in dam safety laws—the research by the HERU engineers with this technology is once again helping NRCS, which has the lead for design and construction of these earthen dams.

The ARS engineers conduct model studies both indoors at small scales and also outdoors at large scales. This summer Hunt will begin using a large-scale flume outdoors that is the actual size of the RCC spillways being designed for these dams. ARS engineers will use the data from the water flow on their experimental spillways to develop design and construction guidelines.

ARS is the principal intramural scientific research agency in USDA.

An assay created by Agricultural Research Service chemist Charles C. Lee and colleagues provides a faster, less expensive way to discover genes that make an enzyme that can help ferment cellulose into biofuel. Click the image for more information about it.

"Superenzymes" could streamline biofuels refining   City trash plus farm leftovers may yield clean energy   Shiitake mushrooms' secret may benefit Earth-friendly fuels

New Test Corners Elusive Biofuels Enzyme

By Marcia Wood
June 25, 2009

In a wood near you, powerful microbes quicken the decay of fallen tree branches. These adroit decomposers perform that essential role by producing specialized enzymes. In the United States and abroad, biofuels researchers prize these enzymes because they may speed and simplify the process of making bioethanol, and coproducts, from the cellulose in the cell walls of energy crops such as switchgrass.

One of the most sought-after of those specialty enzymes may now be easier for today's researchers to find. That's thanks to an assay created by Agricultural Research Service (ARS) chemist Charles C. Lee and colleagues at the agency's Western Regional Research Center in Albany, Calif.

High-speed and high-tech, but surprisingly affordable, the sophisticated assay equips scientists with a faster, less expensive way to discover genes that enable microbes to make an enzyme known as an alpha-glucuronidase. In nature, this enzyme cleaves glucuronic acid from hemicellulose and, in so doing, helps disassemble plant cell walls. Hemicellulose, cellulose and lignin are bound in a tight, complicated matrix that impedes other enzymes' ready access to the cellulosic sugars that are ideal for fermenting into bioethanol.

Right now, there are very few genes in the publicly available GenBank database that code for alpha-glucuronidases. The new assay, however, may change that by making it possible for scientists to quickly screen the genes in masses of anonymous microbes taken from the forest floor, compost heaps, or other outdoor places where decomposers live and work.

In brief, the test involves moving the DNA from the outdoor microbes into laboratory bacteria that, in petri dishes, will form telltale dark spots if they have alpha-glucuronidase genes and enzymes actively working inside. Scientists can then isolate and copy the genes from those bacteria, and perhaps re-tool the genes to make them even stronger and faster-acting, for tomorrow's biorefineries.

Lee developed the assay with Albany colleague Kurt Wagschal, patterning it upon an assay Wagschal built earlier for finding another in-demand biofuels enzyme. Lee also worked with Dominic W.S. Wong, George Robertson, William Orts, and Rena Kibblewhite. All are with the Bioproduct Chemistry and Engineering Research Unit at Albany.

ARS is the principal intramural scientific research agency of the U.S. Department of Agriculture.

A compound produced by the bacterium Bacillus mojavensis, now identified as Leu7-surfactin, could help protect plants, livestock and poultry from fusarium infection. Click the image for more information about it.

New finding helps explain how toxin harms farm animals   Fighting crop-damaging fungi with bacteria

Researchers Identify Inhibitor that Controls Fungal Pathogen

By Sharon Durham
June 24, 2009

A key bacterial compound that inhibits the growth of the plant pathogen Fusarium verticillioides has been identified by Agricultural Research Service (ARS) scientists. The compound could help protect plants, livestock and poultry from fusarium infection.

The compound is produced by Bacillus mojavensis strain RRC101. Finding better controls for F. verticillioides is important because fumonisin mycotoxins—especially fumonisin B1—are toxic to livestock and poultry.

Microbiologist and research leader Charles Bacon and his team at the ARS Toxicology and Mycotoxicology Research Unit in Athens, Ga., identified Leu7-surfactin as the inhibiting compound that controls F. verticillioides. The research team includes microbiologist Dorothy Hinton, chemist Maurice Snook and technician Trevor Mitchell. Their study was published in the April 2009 issue of the Journal of Agricultural and Food Chemistry.

B. mojavensis is a plant-residing bacterium that can be used to control fungal diseases in corn and other plants. Though B. mojavensis is known to work as a biocontrol agent, the specific substance responsible for inhibition of Fusarium was not identified until recently.

The Leu7-surfactin was isolated from growing the bacterium in liquid cultures. In lab tests, the compound proved effective in inhibiting growth of the fungus. Surfactin has a detergent-like activity that dissolves the lipid membranes inside the fungus, eventually killing it.

In Bacon's tests, Leu7-surfactin was effective at controlling F. verticillioides at very low concentrations of 20 micrograms per liter of liquid, making it more efficient to use. In addition to its antibiotic effects, surfactin can be used in textile manufacturing, environmental remediation, and fossil fuel recovery. This compound's properties create great potential for biotechnological and biopharmaceutical applications.

Bacon and his colleagues examined all currently available strains of B. mojavensis and found that all of the strains are endophytic—living within the plant—and all were active against F. verticillioides and other fungi in lab tests. The genus Bacillus is known for the production of more than 24 antibiotics, several of which are fungicidal with the potential to control plant diseases.

ARS is the principal intramural scientific research agency of the U.S. Department of Agriculture.

ARS scientists are seeking to improve sunflowers' resistance to diseases and pests. Click the image for more information about it.

New, disease-resistant sunflower available   ARS diversifies sunflower traits   Scientists collar mystery sunflower pest

ARS Sunflower Research Boosted by New State-of-the-Art Equipment

By Alfredo Flores
June 23, 2009

New, high-yielding sunflower germplasm that gives this important oilseed crop resistance to insects and two fungal pathogens could result from a research effort by Agricultural Research Service (ARS) scientists in Fargo, N.D.

Researchers at the ARS Sunflower Research Unit (SRU) in Fargo, using state-of-the-art equipment, are seeking sunflowers that resist insects and Verticillium and Sclerotinia fungi. Non-oil sunflower seed production was 429 million pounds and valued at $124 million last year in the United States, while oil-type sunflower seed production was just under 3 billion pounds and valued at $545 million.

The SRU scientists, in collaboration with researchers from around the world, have discovered new sources of resistance to these yield-reducing pests. For example, SRU geneticist Brent Hulke has found, with the help of entomologist Larry Charlet and plant pathologist Tom Gulya, unique genes for resistance to downy mildew, rust, Sclerotinia diseases, and two insect pests, the red sunflower seed weevil (RSSW) and the banded sunflower moth (BSM). These genes form the basis for new and improved sunflower breeding lines.

Hulke has developed RSSW- and BSM-resistant germplasm and will test experimental hybrids from these later this year. Preliminary results will be available at the end of the year. This research is greatly facilitated by the efforts of the National Sunflower Association (NSA) and the $400,000-worth of new equipment the NSA donated to the SRU.

Hulke and Charlet are among the ARS speakers at the NSA Summer Seminar that starts today and runs through June 25 in Alexandria, Minn. NSA is a non-profit organization that works on problem solving and creating opportunities for growers and the sunflower support industry.

ARS is the principal intramural scientific research agency in the U.S. Department of Agriculture.