A natural protein from the giant silk moth holds promise as a new way to protect cotton crops from noxious fungi like Aspergillus flavus. The fungus produces a natural carcinogen called aflatoxin that can make cottonseed unfit for animal or human consumption. Proteins called peptides derived from moths or other natural sources are of scientific interest as built-in antifungal agents for genetically altered cotton plants. Preliminary studies show that L-cecropin B, the moth peptide, can kill 100 percent of A. flavus fungi—but only when the fungi don't secrete a potent enzyme that can degrade the peptide. To overcome the problem, scientists rebuilt the moth's peptide, essentially by repositioning certain amino acids that otherwise would succumb to fungal degradation. Later, they exposed laboratory cultures of A. flavus to the rebuilt peptide, D-cecropin B. It not only resisted degradation, but also killed the fungus at concentrations of 5 to 98 parts per million. The peptide has caught the eye of scientists at the National Institutes of Health. They've begun preliminary studies to explore its therapuetic potential to treat fungal infection in humans with weakened immune systems. The peptide may also prove useful in veterinary medicine.
Southern Regional Research Center, New Orleans, LA
Anthony DeLucca, (504) 286-4253, adelucca@nola.srrc.usda.gov

A bacterium without cell walls is behind the poinsettia plant's beauty and popularity as a Christmas favorite, ARS and industry scientists say. Their studies show that the wall-less bacterium, called a phytoplasma, serves as a dwarfing agent that keeps the poinsettia from reaching eight or more feet—the norm in its native Mexico. In the U.S., consumers prefer a short, full-bodied plant about 16 to 18 inches high that can rest atop a table or window sill. The phytoplasma triggers a hormonal imbalance that instructs the plant to form more auxiliary branches. So, it grows outward rather than up. This phenomenon, called free-branching, also produces more of the brilliant red leaf-like structures called bracts. Until recently, scientists suspected the poinsettia mosaic virus as a causative agent. That's because treatments to eliminate it also stop the free- branching trait in the plant. For florists, it's been a love-hate relationship because the pathogen sometimes causes disease that distorts the shape and color of the plant's leaves. Scientists with ARS and Ball FloraPlant of West Chicago, IL, exposed poinsettia mosaic virus for what it truly is: a costly nuisance that plays no part in free-branching. They employed a nonhost plant called periwinkle and a parasitic vine called dodder as a bridge or graft that infects poinsettias with the phytoplasma but not the virus. This led to the first, free-branching poinsettia plants that have phytoplasma, but no mosaic virus.
Molecular Plant Pathology Laboratory, Beltsville, MD
Ing-Ming Lee, (301) 504-6024, imlee@asrr.arsusda.gov

New biochemical tests can demonstrate for the first time the effectiveness of spiders and other predators in controlling several insect pests. ARS researchers have been developing and perfecting tests that use serological analysis—antibodies or custom-designed molecules—in assays to identify the remains of prey in a predator's gut. They say these tests are the most efficient and direct approach to gathering long-term data on spider predation. One test distinguishes cotton bollworms from the tobacco budworm and ground cherry fruitworm. Last year in a Georgia cotton field, the scientists determined that about one-fourth of the specimens of a single spider species had dined on eggs of two cotton pests. In Colorado, they conducted the first North American survey for spiders that kill cereal aphids and other wheat pests. Now, they're developing monoclonal antibodies against three major cereal aphids—the greenbug, Russian wheat aphid and corn leaf aphid. They're collaborating in work on developing monoclonals against the English grain aphid, bird cherry oat aphid and rose grass aphid. With these six antibodies, the scientist will be able to study the role of predators suppressing cereal aphids in many parts of the world. It's part of their ongoing search for more environmentally friendly, economical and efficient biocontrols for insect pests.
ARS Plant Sciences and Water Conservation Research Laboratory, Stillwater, OK
Matthew H. Greenstone, (405) 624-4119, mattg@ag.gov

Plants customize their chemical "distress calls" for help from beneficial wasps, ARS scientists discovered. Scientists have known that some plants emit a chemical SOS to recruit tiny parasitic wasps to rescue them from attacking caterpillars. But such wasps tend to be "host-specific," meaning they are choosy about which insect species they'll sting. Now, studies by ARS and university scientists show that some corn, cotton and tobacco plants emit blends of 10 to 12 different volatile compounds, depending on which caterpillar attacks them. The finding refutes an earlier belief that plants release a general, all-purpose SOS to attract wasps. It could also lead to improving the usefulness of wasps for helping control tobacco budworms and corn earworms. The two pests cost farmers more than a billion dollars annually in losses and chemical controls. In crop fields, plants can emit large chemical plumes to alert wasps to a caterpillar attack. But if the caterpillar isn't a preferred host, the wasp may ignore the signal, subjecting the plant to further damage. To avoid this, plants advertise their attacker's identity with precise mixtures of SOS chemicals. In field experiments, Cardiochiles nigriceps wasps flew more often to plants signaling attack by tobacco budworms, a preferred C. nigriceps host, than to plants infested by corn earworms, a related species. The wasps visited host-signaling plants 164 out of 198 times. Gas chromatography revealed consistent differences between volatiles emanating from these plants and those from plants signaling an earworm attack.
Insect Biology and Population Management Research Laboratory, Tifton, GA
Joe Lewis, (912) 387-2348, wjl@tifton.cpes.peachnet.edu

Beneficial microbes might help tomorrow's honey bees battle the fungus that causes chalkbrood disease. In beehives, the chalkbrood-causing fungus Ascosphaera apis attacks and mummifies bee young—called "brood"—when they are still in the larval stage of their development. In healthy hives, the white, worm-like larvae that hatch from eggs laid by the queen bee develop into cocoon-forming pupae. Young bees later emerge from those pupal cocoons. Larvae attacked by the A. apis fungus, however, may turn into tiny mummies that resemble miniature sticks of white, black or mottled-grey chalk. An ARS microbiologist scrutinized microbes living in hives, stored food and bodies of healthy honey bees in the U.S. and abroad. She isolated and identified certain bacteria, yeasts and molds; they apparently produce compounds that inhibit growth of the chalkbrood-causing fungus. With further study, the most promising of the microbes might become the basis for a commercial product to combat chalkbrood. Chalkbrood causes losses costly to beekeepers, growers and consumers. There is no chemical approved for use in this country for controlling the fungus.
Carl Hayden Bee Research Laboratory, Tucson, AZ
Martha A. Gilliam, (520) 670-6380, ext. 121

The small hive beetle, a honeybee pest, was found in the United States for the first time this year. ARS scientists confirmed the identity of the beetle as Aethina tumida Murray, known to inhabit only South Africa. There, healthy hives easily resist the beetle, which is considered a native species. An alert beekeeper detected the first infested hives in St. Lucie County, FL. The fear is that many U.S. hives already weakened by mites or disease may succumb to the beetles. They don't directly attack the bees; instead, they eat and contaminate their honey, ultimately causing bees to flee the hive. Adult beetles lay eggs in empty hive cells near stored pollen and honey. ARS researchers are advising beekeepers to delay placing extra combs on hives until their bees are actually ready to use them. This practice will help deny the beetles getting "squatter's rights" in unoccupied cells.
Bee Research Laboratory, Beltsville, MD
Jeff Pettis, (301) 504-7299, jpettis@asrr.arsusda.gov

Volatile compounds produced by plants in the Brassica or mustard family suppress growth of soil fungi that cause silver scurf and Verticillium wilt in potatoes. ARS and Cornell University scientists have identified numerous mustards from around the world that produce prodigious amounts of allyl glucosinolate, also called sinigrin. Using these mustards as breeding stock, the researchers hope to produce improved lines that might be grown as a green manure crop in rotation with potatoes. In laboratory studies, allyl isothiocyanate (AITC)—produced as sinigrin breaks down—was particularly toxic to two pathogenic fungi, Helminthosporium solani and Verticillium dahliae. AITC also occurs in cabbage and is primarily responsible for the odor of horseradish. In field studies, the scientists are investigating whether plowed-under black and Indian mustards increase soil fertility while suppressing weeds and soil pathogens. As a rotational green manure crop, mustards might also decrease dependence on synthetic chemical pesticides that could contaminate soil and groundwater.
National Center for Agricultural Utilization Research, Peoria, IL
Steven F. Vaughn, (309) 681-6344, vaughnsf@mail.ncaur.usda.gov

A new biopesticide spray containing some of the armyworm's favorite ingredients could doom this caterpillar pest and curb its costly mischief in corn, cotton and other crops. ARS scientists are testing the biopesticide in greenhouse and field studies as an alternative to chemical insecticides. Their biopesticide contains a mixture of cottonseed oil, sucrose, water and other ingredients that stimulate armyworm feeding. When sprayed onto plant leaves, this coaxes armyworms to ingest more of the spray's other "active" ingredient: a natural insect pathogen called the Anagrapha falcifera nuclear polyhedrosis virus. The virus kills the insect by reproducing inside its gut cells. But the virus poses no danger to humans, wildlife or beneficial insects like bees. In greenhouse experiments, only 22 percent of 378 armyworms survived after chewing collard plants sprayed with the biopesticide. The scientists are also testing sprays containing stilbene brighteners, compounds that help shield the virus from the sun's ultraviolet light. The most effective biopesticide spray may contain a combination of all three ingredients—virus, feeding stimulant and UV "sunscreen."
Insect Biocontrol Laboratory, Beltsville, MD
Robert Farrar, Jr., (301) 504-7319, rfarrar@asrr.arsusda.gov

Two new devices from ARS might boost growers' use of helpful insects and mites and may reduce reliance on chemical pesticides to control crop pests. ARS is seeking a patent for the Aerodynamic Transport Body, or Bugslinger, an innovative modification of skeet or trap shooting targets. Beneficial organisms such as the Aphelinus nr. paramali wasp—which attacks cotton aphids--travel in a lightweight, biodegradable disk, launched from the edge of the field. When the disk lands, wasps fly or crawl out of a small exit. The second apparatus, the Mite Meter, also helps speed and simplify the chore of placing beneficials throughout fields. The Meter features a small tank, insulated to keep an inner bottle chilled. The bottle can be filled with western occidental mites, for instance, to attack Pacific spider mites, strawberry mites, two-spotted mites or other plant pests. Inside the inner bottle, beneficial mites rest among corn grits or other "carrier" compounds. A tiny gate dispenses precise amounts of the mite-and-carrier mix onto the ground. Chilling the mites keeps them subdued, ensuring they won't move away from the gate and will be applied uniformly. (Patent Application No. 08/933,124)
Western Integrated Cropping Systems Research, Shafter, CA
Lyle M. Carter, (805) 746-8004, lcarter@lightspeed.net

Last Updated: November 13, 1998
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