Veterinary, Medical and Urban Entomology
National Program Annual Report FY2003
Introduction
ARS has a long and illustrious history of finding ways to prevent the harm that some arthropods - insects and ticks - do to livestock and people. Indeed, it was ARS scientists who first discovered, in the 1890s, that arthropods could transmit disease, a discovery that led to the eradication of Cattle Fever from the United States. And it was ARS scientists who first developed the sterile insect technique, which resulted in the eradication of screwworm from both North and Central America, who invented the aerosol can (originally for insecticide application by soldiers), who discovered the repellent properties of DEET, and who pioneered the method of treating bed nets with repellents, a tool that now protects millions of children in the tropics from contracting malaria.
Ironically, as the globalization of commerce has grown, the threat to the US from exotic diseases and arthropods has increased. The recent epidemic of West Nile virus (WNV) demonstrates the danger. Like many mosquito-borne viruses WNV is a zoonoses - infecting both animals and people - making it especially difficult to control. WNV was unknown in the US before being detected in New York in 1999, but by the end of 2003 it had spread to all the contiguous states, causing thousands of cases of human and equine illness, and many deaths. WNV must now be considered an endemic disease unlikely to ever be eradicated from the USA. Developing methods to detect, prevent and suppress vector borne diseases is a major effort of ARS scientists, as highlighted by the following selected accomplishments for 2003.
During 2003 those components of National Program 104 that deal with improving our ability to detect and control vector borne pathogens continued to focus on methods to assess and suppress risk. In particular, scientists at the Insect Chemical Ecology Laboratory, Beltsville, Maryland, with support from the Department of Defense, patented SS220, the first insect repellent better than DEET, now 50 years old. Also during the last year the Department of Defense signed a memorandum of understanding with ARS that will infuse up to $3 million per year for the development of innovative means to protect deployed military from vector borne diseases, such as malaria, kala azar and dengue fever. This unprecedented support will greatly enhance ARS’s capabilities and will benefit not only our defense forces but our civilian population as well.
Ticks, which transmit viral, bacterial and parasitic diseases, are especially difficult to control because they are becoming increasingly resistant to available pesticides. The Knipling-Bushland Laboratory at Kerrville, Texas has embarked on a unique project to sequence the genome of the cattle tick, Boophilus microplus, the vector of cattle fever and a host of exotic parasites of livestock. Funding for this project, which has already developed the first large tick expression library with The Institute for Gene Research (TIGR), has been provided by Congress. At the Animal Diseases Research Unit, Pullman Washington, ARS scientists have nearly finished sequencing the genome of the agent that causes bovine babesiosis and are studying Babesia-tick interactions that could be developed into a vaccine. Dr. John George, director of the Kerrville laboratory, received the 2003 Lifetime Achievement Award in Livestock Entomology from Schering-Plough Animal Health.
Besides transmitting disease, some insects directly damage livestock and humans. Although the New World screwworm fly has been eradicated south to the border between Panama and Colombia, ARS scientists are engaged in finding ever more effective means to prevent it from reestablishing. During early 2003, a global information system (GIS) model developed by an ARS scientist played a key role in suppressing an epidemic in Mexico. At the Red Imported Fire Ant Unit, Gainesville, Florida, Dr. Stephen Valles and colleagues have formed the first DNA expression library for the fire ant and used it to discover the first viruses in the ants, a finding that could lead to new biological control agents.
Administratively, peer reviews were conducted in 2003 of the Midwest Livestock Insects Research Unit, Lincoln, Nebraska; the Arthropod Borne Animal Diseases Laboratory, Laramie Wyoming; and the Mosquito and Fly Research Unit, Gainesville, Florida. National planning workshops with stakeholders were held at New Orleans and Denver, and the National Action Plan for NP 104 was rewritten, in preparation for each unit’s new five year plan, to be reviewed by the Office of Scientific Quality Review in 2004.
Mosquitoes and Biting Flies
Tools for Prevention - ARS has worked with the Department of Defense to produce better methods of personal protection against mosquitoes since World War II. Repellents are especially important because there are still no vaccines against such dangerous mosquito borne diseases as malaria and dengue. An important result of this collaboration was the discovery of DEET, still the most effective commercially available repellent. The effectiveness of DEET, however, is limited by the fact that it degrades most plastics and does not repel some important vector species encountered outside the US. In 2002, a US patent was granted to ARS scientists of the Chemicals Affecting Insect Behavior Laboratory, at Beltsville, Maryland for the discovery of a new class of repellent (“SS-220”) superior to DEET. With support from DOD and the collaboration of Walter Reed scientists, SS-220 successfully passed the first battery of toxicity tests necessary for EPA approval and could be available to American troops by 2004.
Tools for Surveillance Effective response by public health officials to epidemics of native or introduced vector-borne disease depends on knowing what the problem is and where it is. Ideally, measures for prevention are begun when indicators predict an epidemic, before the first cases appear. There is an urgent need for better methods of surveying for disease vectors. In particular, cheaper, more portable, more trouble free traps are needed. ARS scientists at the Mosquito and Fly Research Unit, Gainesville, Florida are engaged in testing new WNV surveillance traps with the Connecticut Agricultural Experiment Station. MFRU also tested the treated uniforms of Marines returning from Liberia for repellent activity and embarked on a Department of Transportation initiative to develop air curtains for international commercial aircraft.
Tools for Control - Dr. James Becnel, of the MFRU, Gainesville, is developing a native baculovirus pathogenic to mosquito larvae as a potential biocontrol agent. He has sequenced two viruses, one that specifically attacks only Anopheles mosquitoes and one only Culex, and has determined the cation concentration of the water to make them most toxic to mosquitoes.
Tick Research
Tick Genome - No tick or related arthropod has yet been sequenced and the size of the tick genome - more than one billion nucleotides - will be an expensive challenge. Nevertheless, the economic and health significance of ticks makes it a priority. The ARS, with Congressional sponsorship, has taken the lead in coordinating an international effort to sequence the tick genome, and organized sequencing of Boophilus microplus involving researchers world wide. In 2003 the first library of 20,000 clones of expressed genes was produced and is now being analyzed. By the end of 2004 it is estimated that three times that number will have been isolated.
Control of Lyme Disease - Ixodes scapularis, the vector of Lyme disease, feeds predominately on white-tail deer. ARS scientists in Kerrville patented an invention (the ‘4-Poster’) that uses bait to encourage deer to self-apply pesticide to their heads, where most ticks feed. ARS and university scientists in Connecticut, Maryland, Rhode Island, New Jersey and New York successfully completed the third year of a Congressionally supported five year project to test the 4-Poster in the reduction of ticks. In test plots there has been a 63% average reduction in Lyme disease risk, with each 4-Poster having an effect over four square miles. this is the first demonstration of area wide control without using broadcast application of insecticide.
Screw worm and Flesh Flies
Screw worm once plagued the US livestock industry throughout the South. A remarkable conceptional breakthrough, and equally remarkable practical follow-up, by Dr. E. Knipling and Raymond Bushland of ARS led to the eradication of this pest from North and Central America through the release of overwhelming numbers of sterile male flies. ARS scientists work at Lincoln, Nebraska and in Mexico and Panama supporting the APHIS eradication effort. Work is proceeding at Lincoln on producing a transgenic male-only strain after the successful proof that screwworm can be genetically transformed. Plans are underway to consolidate all screwworm research at new facilities in Panama by 2005.
Termites and Imported Fire Ants
The Formosan subterranean termite (FST) causes more than $1 billion damage per year to houses, piers, railway ties and trees throughout the Southeast and Hawaii. Unlike native termites, the FST builds large colonies underground and infest trees, making control difficult. In 2003, the area-wide termite management program conducted in the historic New Orleans French Quarter by a consortium led by ARS scientists from the Southern Regional Research Center and funded by Congress was expanded from 15 to 30 blocks. Smaller collaborative trials are being carried out elsewhere in Louisiana, Mississippi, Hawaii and Texas. A portable acoustical device developed by collaborators at the University of Mississippi has proved especially successful at detecting infestation in trees, now believed to be an important refugia. A new attractive bait, using a naptholene analog, was patented and is now undergoing commercial development.
Fire ants now infest more than 320 million acres in the American Southeast, California, New Mexico and Arizona. Damages exceed $5 billion dollars a year. Fire ants reduce crop yields, damage electrical equipment, and injure or kill young domestic and wild animals. More than 30% of people living in infested areas are bitten and about 1% have severe allergic reactions. ARS scientists at the Fire Ant and Household Pest Research Unit, Gainesville, Florida have used a microbe, Thelohania solenopsae, several tiny species of parasitic fly discovered in South America, and chemical baits in an integrated pest management plan to suppress colonies more than 90% in a large controlled trial in South Carolina. Three additional species of phorid fly were discovered in Argentina and are now being tested or completing quarantine. Anew fungal pathogen, yellow head, and two previously unrecognized viruses have also been isolated and will be given to collaborators in Texas, Louisiana, Mississippi, Georgia, South Carolina and Florida for testing.
