A state-of-the-art scanning electron microscope mounting technique that uses low temperature (LT-SEM) may help researchers better understand how parasitic mites like Varroa interact with their bee hosts. Varroa mites feed on the blood of adult and developing young bees. Parasitized bees may have deformed wings and abdomens and a shorter life span than their unparasitized hivemates. Because the LT-SEM freezes and captures the Varroa mites on bees at the moment they are parasitizing them, a team of ARS scientists has discovered some intriguing behavioral and morphological patterns. The technique has shown that Varroa mites may be camouflaging themselves by aligning their setae (their tiny hairs) with the hairs on the bee's body. By doing this, they may escape detection when the bee grooms itself or is groomed by another. If this hypothesis is correct, it may be possible to breed bees that more easily detect mites and aid their removal from their bodies. LT-SEM technology provides an exciting new tool that will be used to reveal the exact types and behavior of mites. It is already providing valuable new information that could be used to control mites as agricultural pests or to enhance their efficacy as biological control agents.

Bee Research Laboratory, Beltsville, MD
Jeffery S. Pettis, (301) 504-8205, pettisj@ba.arsusda.gov

Systematic Entomology Laboratory, Beltsville, MD
Ronald Ochoa, (301) 504-7890, rochoa@sel.barc.usda.gov

A team of plant physiologists is studying a tiny mite as a possible biological control for Canada thistle, a major invasive weed pest in U.S. pastures. First identified in Europe more than 100 years ago, this mite, (Aceria anthocoptes), was discovered in the United States in 1998, when scientists collected some Canada thistle, (Cirsium arvense), on Maryland's Eastern Shore. Preliminary results from a survey of the area and surrounding states indicate the mite is abundant there and specific for Canada thistle. Under growth-chamber conditions, mite populations on a Canada thistle plant can reach very high levels and cause severe damage. Their presence leads to a reddish-brown discoloration and curling of leaves and spindly growth. They can also transmit plant diseases to the weed. The mite was identified and characterized using state-of-the-art scanning electron microscope mounting techniques that use low temperature. The scientists hope to learn whether mite populations in the field can be manipulated to significantly curb Canada thistle growth and if the mite can transmit viruses to the weed that could also impede its growth. A search for viral-infected Canada thistle plants in the areas where they were once reported—Denmark, England, and North Dakota—is under way. The team also plans to further examine the specificity of A. anthocoptes.

Sustainable Agricultural Systems Laboratory, Beltsville, MD
John Lydon, (301) 504-5379, lydonj@ba.ars.usda.gov

Systematic Entomology Laboratory, Beltsville, MD
Ronald Ochoa, (301) 504-7890, rochoa@sel.barc.usda.gov

The Parkinsonia seed beetle could serve as a biological control agent for the Jerusalem thorn tree, an invasive plant that has spread across rangelands from southern Texas to Arizona and northern Mexico. ARS researchers have found that the Parkinsonia seed beetle, Penthobruchus germaini, may be able to control the spread of this invasive tree, Parkinsonia aculeata, by depositing its eggs in the tree's seedpod. Once the eggs hatch, the larvae burrow into the seeds to feed and complete their development. In field studies, the beetle was found to infest one out of every four seeds in one season. Since P. germaini also develops in the relatively short time period of 48 days, two generations of beetles would be available as biological control agents each year. Its cold tolerance, high egg fertility, and low rate of natural parasitism are also highly desirable attributes. And the tests indicate that the beetle is host-specific to P. aculeata. Preliminary field evaluations in Australia—where P. germaini was introduced in 1995—indicate that the beetle is destroying a high percentage of Jerusalem thorn tree seeds there.

South American Biological Control Laboratory, Buenos Aires, Argentina
Juan Briano, 54-11-4662-0999, jabriano@mail.retina.ar

A fungus new to science that may control ragweed has been discovered. Ragweed, Ambrosia artemisiifolia, is a noxious plant that infests thousands of acres of arable land worldwide and causes allergic reaction—often seasonal—in many people. Its pollen causes many sufferers irritated eyes, runny noses, and general discomfort. Last year, scientists in Hungary—where ragweed is even more of a problem than in the United States—reported they had found a species of Septoria fungus that was pathogenic to ragweed. It causes the leaves to die and kills some plants, probably by entering through their leaf openings, called stomates. ARS mycologists discovered that the fungus belongs to the asexual genus Septoria. After searching the literature, they determined that this fungal species, also found in the United States, had never been described. They characterized it using molecular sequencing, named it S. empambrosia, described and illustrated it, and showed that it is distinct from three other related known Septoria species. Scientists will use this information to communicate about the new fungus in developing it as a biocontrol agent for ragweed.

Systematic Botany and Mycology Laboratory, Beltsville, MD
David F. Farr, (301) 504-5364, dave@nt.ars-grin.gov

Land managers can now compare lists of noxious weeds from the lower 48 United States and 6 Canadian provinces by logging on to a new section of the University of Montana's "Invaders" web site. ARS scientists developed the new noxious weed section at the web site: http://invader.dbs.umt.edu/Noxious_Weeds This tool will help decision-makers prioritize control and research efforts at local and national levels. In addition, they can use the system to predict potential future problems by examining lists from neighboring states or regions. Significant amounts of money and effort could be saved by managing invasive weeds while infestations are still small. The ARS researchers' next step is to look at weed distributions and how alien weeds have spread over time. Spotted knapweed, for instance, first entered the Pacific Northwest around 1893. It began to spread more rapidly in the 1950s, but distribution exploded from 60 counties in 1985 to at least 175 today. The researchers hope to identify reasons for such expansions, as well as trends that can help identify which alien plants pose the most risk of future expansion.

Northern Plains Agricultural Research Laboratory, Sidney, MT
Kerri Skinner, (406) 433-9484, kskinner@sidney.ars.usda.gov

Bacteria discovered near the roots of sugar beet plants may offer biological alternatives to chemical pesticides for controlling one of this crop's worst fungal enemies. Ongoing ARS studies have shown that certain strains of Pseudomonas root bacteria exude substances that stifle the growth of Cercospora beticola fungi. In nature, the bacteria compete with the fungi for space and nutrients on or near sugar beet leaves. Cercospora causes the sugarbeet disease leaf spot, which weakens susceptible cultivars by defoliation. Grown on 1.5 million acres, sugar beets supply an estimated 50 percent of America's sucrose. Beets that are somewhat genetically resistant to Cercospora have been identified, but they haven't been developed into elite commercial lines. Therefore, beet growers are forced to rely on chemical fungicides to reduce the economic impact of Cercospora outbreaks. Scientists are exploring a more environmental friendly approach using two kinds of Pseudomonas bacteria: ND6-2 and ND9L. One strategy is to mix the bacteria's spores into a so-called biopesticide that could be sprayed onto the beet plant's leaves to prevent Cercospora fungal spores from germinating. Another approach is to isolate genes for the microbe's antifungal compounds and transfer these genes into sugar beets.

Molecular Plant Pathology Laboratory, Beltsville, MD
David Kuykendall, (301) 504-7072, dkuykend@asrr.arsusda.gov

A small, parasitic wasp could play a major role in efforts to improve the quality of U.S. stored commodities. Stored-product insects can be a major problem in grocery, health food, pet stores, and home pantries. Infested products can include bird seed, peanuts, pecans, dog food, candy, macaroni, breakfast cereals, cornmeal, bread, and dried beans. Habrobracon hebetor is a beneficial parasitic wasp that attacks the larvae of many agriculturally destructive moths, including the Indianmeal moth—the most damaging insect pest in stored commodities. This moth as well as other insect pests has developed widespread resistance to Bacillus thuringiensis (Bt), which means pesticides must be used to control them. New biocontrol methods are needed because insects are also developing resistance to currently available pesticides, and environmental regulations limit the use of others. Quantities of H. hebetor are commercially available for pest management programs, but they would be more economical to mass-produce if artificial diets were available. ARS researchers described the digestive processes of these parasites as they fed on the blood of Indianmeal moth larvae in the laboratory. Information from this research will aid in the development of artificial diets.

Grain Marketing and Production Research Center, Manhattan, KS
James E. Baker, (785) 776-2785, baker@usgmrl.ksu.edu