USDA ARS National Program 104:
Veterinary, Medical, and Urban Entomology
Annual Report for Fiscal Year 2006
- Introduction: 2, 4, 6, 8
- Component 1: Ecology and Epidemiology
- Component 2: Detection and Surveillance Technology
- Component 3: Biology and Physiology
- Component 4: Control Technology
Introduction: 2, 4, 6, 8 Protecting the two- and four-legged from the six- and eight-legged.
Agriculture depends on people, animals, and plants. National Program 104 solves problems that affect people and animals, protecting them from the insects and ticks that cause direct injury or disease. The program is particularly well suited to the mission of the Agricultural Research Service because research in this area that addresses livestock problems often also solves human problems and vice versa. For example, the invasive imported fire ant causes discomfort, injury, or sometimes severe illness in almost half of the population of 11 states, but it also affects livestock through direct injury and the destruction of pasture land. Another example is the threat of the introduction of Rift Valley fever virus into the U.S. This threat that has been brought into sharp focus by the incipient outbreak in Kenya in December, 2006. This outbreak was predicted by ARS scientists in October based on weather patterns and satellite images of plant growth. Mosquitoes would transmit this virus to ruminant livestock, disrupting the industry in large regions of the country. Humans could suffer severe illness from infections caused by mosquito bites or by exposure during meat production.
ARS has a long history of achievement in this field. In fact, the first discovery of a disease-causing pathogen transmitted by an arthropod was performed by the microbiologist, Theobald Smith, in 1889-1893 while working for the U.S. Department of Agriculture. He found that Texas cattle fever was caused by a protozoan and that the protozoan was transmitted between cattle by a particular kind of tick. Smith’s discovery was well-documented and often discussed at the time, leading to the astoundingly significant association of malaria, yellow fever, and dengue to mosquitoes. His discovery also led to an eradication campaign started in the early 1900s that continues to this day, almost eliminating the threat of Texas cattle fever in our country. The importance of mosquitoes as vectors of important diseases caused a renewed interest in accurate taxonomy and, again, USDA was at the center of activity. L.O. Howard, H.G. Dyar, and F. Knab produced the definitive scholarly work on mosquitoes of the Americas, with Knab completing the manuscript in 1918 as he was dying from sand fly-borne leishmaniasis. In 1942 the War Department called on the USDA to develop new insecticides and repellents to protect military personnel from the ravages of scrub typhus and malaria, particularly in the Pacific Theater. Scientists at the Orlando laboratory eventually screened over 20,000 compounds and produced a series of compounds that could be applied to the skin or clothing. Before the introduction of chloramphenicol in 1949, scrub typhus was almost a death sentence and the repellents dimethyl phthalate, ethyl hexanediol, and benzyl benzoate were all that stood between soldiers and this infection. Thanks to USDA scientists Carroll Smith and Harry Gouck, the screening effort in the 1950s found that DEET was a highly effective insect repellent. DEET remains the standard repellent active ingredient today. ARS also developed the current repellent treatment for military uniforms during the 1980s. The Department of Defense has again asked ARS to produce better products to protect the U.S. military and the agency has responded with a major effort.
No discussion of USDA achievements would be complete without mentioning the research that led to the defeat of the screwworm fly. This fly actively seeks even the smallest wounds in cattle, lays its eggs, and then causes what is often mortal injury to the animals. In 1950, E.F. Knipling began an effort to release sterile males of the fly over huge areas, preventing the females from laying fertile eggs. This technique has been refined greatly over the years, but it continues and has successfully eradicated the fly as far south as Panama. The benefits from this program are almost incalculable, considering the economic benefit to the American beef industry, the relief from animal suffering, and the benefit to small landholders in Mexico and Central America.
Two significant discoveries in 2006 emphasized the importance of fly control. A study by a CSREES collaborator at Kansas State University, Dr. Ludek Zurek, showed definitely that house flies could acquire the O157:H7 toxigenic Escherichia coli bacteria (the strain associated with raw vegetables and hamburger that causes severe disease) from cattle feces. Simply releasing those flies in the presence of an uninfected cow transmitted the infection to the animal within two days. The other discovery was by Dr. Christopher Geden from the Mosquito and Fly Research Unit, Gainesville, Florida. He worked with scientists at the Southeast Poultry Research Laboratory to demonstrate that chickens fed house flies infected with Salmonella enteriditis picked up the infection. These findings indicate that fly control would reduce the occurrence of these pathogenic bacteria in the U.S. food supply.
In 2006, National Program 104 continued an active agenda of research based on its five-year plan started in 2003. The program includes 20 core-funded projects performed at 10 locations in Florida, Maryland, Nebraska, Mississippi, Louisiana, Texas, Wyoming, Washington, and Panama. Fifty-one permanent party scientists have contributed to 80 peer-reviewed scientific publications. In the course of this work they have collaborated with 25 universities and 10 industrial partners. In the course of this work, NP 104 scientists proposed seven invention disclosures, established one new cooperative research agreement, and 10 new material transfer agreements. Three of our laboratories worked closely with the Department of Defense under the Deployed Warfighter Protection Program to develop new products for the protection of deployed military personnel against the dangers of insect-borne pathogens that cause disease.
Some of the achievements of 2006 are briefly described below categorized according to the NP 104 Action Plan, written in 2003. The accomplishments cut across the efforts of individual laboratories, demonstrating a level of integration within the program.
Component 1: Ecology and Epidemiology
Ecoepidemiology at Yale University. The ARS tick program is fortunate to have the cooperation of the Center for Ecoepidemiology, Yale University, New Haven, Connecticut. Their work addressed risk assessment of the etiologic agent of Lyme disease, Borrelia burgdorferi, and its vector tick, Ixodes scapularis. They found that deficiency of a protein in the ticks makes them more susceptible to infection with the Lyme disease agent. They also studied the coevolution of the tick and the Borrelia, working toward an understanding of the risks of new pathogens. Evaluating the distribution of Lyme disease in the northeastern U.S., they found that forest fragmentation favors transmission and explored the relationship between climate change and the ecology of Lyme disease.
Ecology of termites following Hurricane Katrina. The center of ARS research on termites is New Orleans, so they were heavily affected by Hurricane Katrina. Remarkably, the Formosan Subterranean Termite Research Unit had a very productive year. The hurricane was the occasion for a disturbing, though biologically interesting discovery. The New Orleans Mosquito and Termite Control Board collaborated with FSTRU to document that 20% of stumps in one area and 21% in another maintained viable colonies of the Formosan subterranean termite despite the flooding of New Orleans. Although the biological mechanism remains unknown, some of those colonies lived through conditions as harsh as submersion under brackish water, sometimes up to fifteen feet deep, and up to three weeks in duration.
Epidemiology of bluetongue virus. Some species of these small flies, also called no-see-ums or sand flies, are important vectors of viruses to livestock. Scientists at the Arthropod-Borne Animal Diseases Laboratory in Laramie, Wyoming, showed that the strains of Culicoides sonorensis in Montana and Alberta (Canada) were not capable of transmitting blue tongue virus. The occurrence of blue tongue virus can cause considerable complication to the movement of animals, as well as direct damage to some species. This discovery changes the assessment of risk resulting from movement of infected animals into this region. This work was accomplished using the latest genetic techniques and with the cooperation of Agriculture Canada. The laboratory also worked on another virus that is a problem for U.S. agriculture, vesicular stomatitis virus. In response to an unprecedented outbreak of the disease in Wyoming, scientists collected a wide variety of insects to determine whether more than black flies and Culicoides are capable of transmission.
Component 2: Detection and Surveillance Technology
Targeting mosquitoes for control. The threat of mosquito-borne diseases that already exist in the U.S., like West Nile, or disease that might be introduced, like Rift Valley fever, has raised awareness of the need for community mosquito control. Each mosquito abatement district tends to know its own area well, but areas between districts or areas where new districts should be formed, may have large concentrations of mosquitoes in some parts but not in others. Scarce control resources need to be targeted according to the threat. Scientists at the Mosquito and Fly Research Unit, Center for Medical, Agricultural, and Veterinary Entomology and the Arthropod-Borne Animal Diseases Research Laboratory, working in cooperation with academia, mosquito abatement districts, state governments, and other federal agencies, have assembled a series of models of mosquito distribution that range from continental to local scale. Combined with temperature-based models of disease transmission risk, these models form a picture of relative risk for the entire Nation. Following further development and distribution, these models will be an essential tool for decision makers who have to put mosquito control resources in areas that will have the greatest impact against disease transmission.
New tools to detect mosquitoes and their pathogens. Progress in research on surveillance either contributed to the measurement of mosquito populations or to the pathogens within mosquitoes. The Mosquito and Fly Research Unit, Gainesville, Florida, showed that the particular stereoisomer of an attractant chemical can influence its effectiveness. They also identified new mosquito oviposition attractants. In field work, the MFRU quantified some of the relationships between trapping results, temperature and light levels. The Arthropod-Borne Animal Disease Research Laboratory, Laramie, Wyoming, and Suffolk County, New York, Department of Health doubled the sensitivity of PCR detection of West Nile virus by adding proteinase K to the extraction procedure. An entirely different method of detection used by the University of Wyoming School of Pharmacy uses desorption ionization-mass spectroscopy to characterize proteins amino acid by amino acid. Adding “buckey balls” carbon (buckminsterfullerene) improved detection by increasing desorption from a surface.
A step forward in understanding stable flies. The Midwest Livestock Insect Research Laboratory, Lincoln, Nebraska, showed that a commercial trap captured twice as many stable flies as the standard alsynite (a fiberglass material) trap. This result was significant because many studies of stable fly distribution are based on data from alsynite traps, a technique that probably leads to erroneous conclusions.
Keys to extinguishing fire ants. The National Biological Control Laboratory, Stoneville, Mississippi, worked on detection of fire ant mounds using aerial photographs and other remote sensing technology. Multispectral data were capable of detected 79% of fire ant mounds. They applied for two patents on point sensor technology and described the distribution of the ants in Christmas tree plantations. Working with Alabama A&M University and an industrial partner, they described the thermal signature of a fire ant mound, and then used that information to find infested areas. In another approach, the NBCL collaborated with the University of Mississippi on studies of sounds produced by fire ants. They measured wing beat frequencies of alate ants (those that establish new colonies). On a genetic level, scientists collected 3,281 ants from 363 mounds and amplified microsatellite DNA, preparatory to determining the interrelationships of individual colonies. NBCL found a genetic allele associated with colonies of red and black fire ant hybrids (Solenopsis invicta x richteri) that appear to be a marker for polygyne (multiple queen) colonies. They also sponsored work on the taxonomy and distribution of native ants in the Southeast, some of the results of which can be viewed at http://www.msstate.edu/org/mississippientmuseum.
Component 3: Biology and Physiology
Cutting edge research on tick physiology. Ticks are a major threat to the livestock industry and to human health because particular species transmit pathogens that cause serious diseases. Some of those diseases are already a problem and others could be introduced to the United States with disastrous results for the agricultural economy. Scientists at the Knipling-Bushland U.S. Livestock Insect Research Laboratory, Kerrville, Texas, and at the Areawide Pest Management Unit, College Station, Texas, in collaboration with academic institutions and industry, have looked deep within the mechanics of tick physiology to discover the DNA sequences responsible for pesticide resistance, susceptibility to disease transmission, and essential metabolic processes. This work has opened an entirely new range of possibilities for tick control. Salivary components of ticks have been identified and genetically defined, creating candidates for anti-tick vaccines. Scientists described the first signal transmitter chemicals of the tick brain, establishing a new mode of action for toxicants. The sequence of genes that produce insecticide resistance enzymes was the basis for the development of rapid tests to determine an infestation’s susceptibility to a particular treatment. The products of this research provide the advances necessary to maintain the current barrier against cattle fever, keep diseases like heartwater out of the U.S., and prevent tragic human illness from Lyme disease and other pathogens.
Discovered details of biting midge saliva. Biting midges transmit bluetongue and vesicular stomatitis viruses to cattle and other ruminants. These infections affect the health of the animals and also greatly complicated what should be routine movement of animals for trade. Scientists at the Arthropod Borne Animal Diseases Research Laboratory in Laramie, Wyoming, have accomplished the nearly impossible by extracting saliva of these tiny insects and then analyzing its components. The result has been an impressive variety of proteins, many of which have strong physiological effects on mammals that are bitten. These basic discoveries will lead to new ways to protect cattle from biting midges and possibly even provide better control techniques for species that bite humans.
Component 4: Control Technology
Control of fire ants without chemicals. Imported fire ants ruin pasture land, disrupt agricultural work, and seriously injure people over an area of 300 million acres in fifteen states and Puerto Rico. Scientists at the Imported Fire Ant and Household Insects Research Unit, Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, Florida, and at the National Biological Control Laboratory, Jamie Whitten Delta States Research Center, Stoneville, Mississippi, have greatly expanded the usefulness of biocontrol agents (insects and pathogens that kill fire ants). They have continued to facilitate the distribution of tiny flies that parasitize the ants, documenting their spread in Alabama, Oklahoma, and Tennessee, as well as adding a fourth species of fly. Scientists have characterized the first virus ever discovered in fire ants and discovered a new species of roundworm that kills the ants. Workers are searching in South America for new biocontrol agents and using modern genetics to match those organisms to populations of fire ants. As the new insect and pathogen enemies of fire ants become established across the southeastern United States, they will form a natural complex that will lower the number of fire ants to more tolerable levels. As the number of fire ants is reduced, native ants will move into unoccupied habits, providing further control and improving biodiversity.
New insecticides to protect deployed warfighters. Military personnel deployed overseas are particularly susceptible to disease and some of the most important diseases for the military are transmitted by insects, ticks, or mites. ARS scientists have been funded by the Department of Defense to work toward development of new insecticides for public health use by looking at existing pesticides and by inventing new ones. Working at the Chemicals Affecting Insect Behavior Laboratory, Plant Science Institute, Beltsville, Maryland; the Mosquito and Fly Research Unit, Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, Florida; the Areawide Pest Management Laboratory, College Station, Texas; and the Formosan Subterranean Termite Research Unit, Southern Regional Research Center, New Orleans, Louisiana, chemists and entomologists have invented four entirely new insecticidal chemistries and discovered that two existing pesticides might have good public health application. By performing the basic work to identify new insecticides and test the range of their use, ARS will be able to hand off chemicals to industry for development and marketing. The military will be able to use these new, registered insecticides to make the environment safer for deployed forces.
Successful biological treatment of termites in living trees. The Formosan Subterranean Termite is a devastating pest of property and trees, nesting in the ground, in walls, or in living trees. Treatment of trees is particularly difficult because of poor access to the interior and the challenge of detecting the termites within. ARS scientists at the Formosan Subterranean Termite Research Unit at the Southern Regional Research Laboratory, New Orleans, Louisiana, working in collaboration with academia, industry, and local government, performed research showing that termites could be detected from their unique head-bumping sounds. A device was developed to listen for the termites in trees, which was successfully applied to show that 60% of trees in a portion of New Orleans were infested. Trees were successfully treated with a keratin-based foam containing spores of an insecticidal fungus. This procedure was developed start to finish by ARS and provides the pest control industry with a safe, efficient way to eliminate Formosan Subterranean termites from trees. Combined with other control techniques, this development increases the possibility of significantly reducing termite populations in local areas.
Reduction in environmental and monetary costs of sterile screwworm production. The screwworm fly was a devastating pest of cattle and other livestock throughout the southern and central U.S. up until the 1950s. At that time, the USDA organized a bold plan to eliminate the fly by releasing billions of sterile male flies, overwhelming the reproductive systems of the species. The program has progressed to the point that the screwworm fly has been eradicated all the way south to Colombia. To maintain this barrier, billions of flies must be reared, sterilized, and released. Until this year, the diet for rearing the immature flies (maggots) included a gelling agent that made the mix palatable to the flies. The gelling agent was expensive and had to be disposed as hazardous waste. ARS scientists working at the Screwworm Research Unit in Tuxtla-Gutierrez, Mexico, developed a cellulose-based diet that used ground-up newsprint instead of the gelling agent. The diet has been adopted by the fly-production plant and saves approximately $300,000 per year, as well as avoiding an environmental problem.
New ways to control horn flies. Horn flies are a particularly nasty pest of cattle. They ride along on the cow taking frequent bloodmeals, only leaving to quickly lay eggs on a fresh cow pat. Some estimates attribute over $700 million in damage to cattle per year to this fly in the United States. Current control techniques rely on liberal use of insecticide, frequently failing because of the development of resistance. ARS scientists at the Knipling-Bushland U.S. Livestock Insects Research Laboratory, Kerrville, Texas, have gone a long way toward finding new ways to control horn flies. They have assembled a database of cattle DNA associated with either susceptibility or lack of susceptibility to horn fly. They collaborated with the Areawide Pest Management Research Laboratory, College Station, Texas, to discover a brain signal chemical that performs essential physiological functions in the fly. Finally, they were able to control the fly by dusting cattle with the spores from a fungus that is toxic to the insect but not the cow. These discoveries will lead to more sophisticated control techniques that will be combined to perform sustainable, environmentally friendly pest management of the horn fly.