Page Banner

United States Department of Agriculture

Agricultural Research Service


Location: Mosquito and Fly Research Unit

2009 Annual Report

1a.Objectives (from AD-416)
1) Develop new pathogen delivery formulations and molecular methods based on pathogenic viruses for control of mosquitoes. 2) Improve parasitoid-based management systems for control of filth flies. 3) Test and develop new and improved pesticides and "attract and kill" systems as management tools for pest and vector species. 4) Discover, evaluate and develop new personal/animal protection tools.

1b.Approach (from AD-416)
Identify and evaluate novel biologically based and self-sustaining biological control agents for mosquitoes and flies; incorporate these into integrated management strategies and demonstration projects. Isolate, identify and validate the efficacy of repellents under laboratory and field conditions to develop new strategies for personal/animal protection from disease vectors and nuisance species. Discover and develop leading candidate compounds from critical screening to targeted applications, to identify new insecticides and more efficacious toxicants for control of mosquitoes and flies.

3.Progress Report
The overall goal of this research project is to develop components for integrated mosquito and fly management programs including personal/animal protection systems. Integrated management systems: Research was conducted on discovery of new toxicants for control and pesticide delivery technology. Larval and adult screening of compounds against mosquitoes has provided essential information on toxicity for conducting structure activity analysis. The toxicities of 33 carboxamides were determined and structure-activity analysis of the carboxamides can be used to make modifications and develop new insecticides. In order to access their insecticidal activity, the relative toxicities of 8 repellents for 4 different species of mosquitoes were evaluated. Molecular techniques have identified 18 different genes isolated from a permethrin-treated Aedes aegypti subtractive library. Eight of these genes were determined to be highly expressed and can be targeted using newly developed technology (RNA interference) for insecticide resistance management and/or toxicity. Methods to improve effectiveness of currently used adulticides through improved delivery technologies were examined. Evaluation of an excito-repellency compound found that it did increase the speed and duration of flight with higher mortality. Field trials of barrier treatments with two synthetic pyrethroids were conducted in multiple environments to assess efficacy against natural mosquito and sand fly populations. The results suggest that barrier treatments may be successful in providing protection from vector-borne diseases for deployed troops in desert habitats. The effectiveness of imidacloprid-treated visual targets placed around a calf barn for house fly exclusion was evaluated. A significant reduction in the number of flies entering the barn was found when treated targets were in operation. Studies on a salivary gland hypertrophy virus specific for house flies found that the most effective method for deploying the virus may be treatment of fly resting sites. Personal/animal protection systems: Research was conducted on compounds that interrupt vector-host contact and the effectiveness of permethrin-treated uniforms for military personnel. A technique was developed which allows both the toxicity and spatial repellency actions of a chemical to be evaluated under semi-field and field conditions. The ability to quantify these chemical actions is critical for the development of innovative vector control strategies. A laboratory comparison of 3 attraction-inhibitors against sand flies was conducted in Egypt. It was demonstrated that all three chemicals suppress host-seeking behavior. The bite protection levels of permethrin-treated Fire Resistant Army Combat Uniforms (FRACUs), Air Force Battle Uniforms (ABUs), and U.S. Marine Corps Fire-Resistant Organization Gear (FROG) were determined. This information is critical for the military to assure high quality standards for the effectiveness of treated uniforms to protect deployed troops. MFRU SYs played leadership roles with other international experts in the development of World Health Organization (WHO) guidelines for insecticides and repellents.

1. Residual barrier treatments on native vegetation and artificial substrates in desert, tropical, and sub-tropical habitats for control of mosquitoes and sand flies. MFRU staff carried out field trials of barrier treatments in multiple environments to assess efficacy against natural mosquito and sand fly populations. Four styles of U.S. military desert and woodland camouflage netting and tent systems, any of which could be routinely provided to current U.S. military units, were treated with one of two synthetic pyrethroids (bifenthrin and lambda-cyhalothrin) and set out in two desert environments. In addition, naturally occurring desert xeric vegetation in the Coachella Valley site in California was treated with a residual barrier of bifenthrin on two occasions.. One cold mist conventional backpack sprayer was used for all treatments of artificial substrates, but a variety of cold mist and electrostatic sprayers was used for the two vegetation treatments. Efficacy of barriers was assessed in the field with a schedule of regular overnight mosquito population sampling within and outside of treated and untreated netting perimeters using a variety of traps. Efficacy of treated barriers was assessed in the lab by measuring mortality in bioassays on temporal samples of cut vegetation or material using colony-reared female mosquitoes. Overall results from vegetation treatments indicated a significant reduction in mosquitoes in field counts and lab assays for up to 1 month; overall results of material treatments indicated significant reduction mosquitoes or sand flies in field counts and lab assays for up to 8 months. The results suggest that, as an enhancement to the current DoD pest management system barrier treatments may provide protection from vector-borne diseases for deployed troops in desert habitats by significantly reducing densities of mosquitoes or sand flies.

2. Bite protection evaluation of permethrin-treated United States Military Uniforms: (a) Determined the bite protection levels of factory-treated Fire-Resistant Army Combat Uniforms (FRACUs) that were treated by two different contractors. The bite protection levels of the untreated and laundered uniforms were used to set the detail specifications for "First Article" submissions for contractors to supply the U.S. Army with FRACUs as they transition from field treatment to factory-treated uniforms. The composition of the FRACU (65% rayon, 25% para-aramid, 10% nylon) and high air permeability (55 cubic feet per minute) presented significant challenges to permethrin retention in the uniform and efficacy (bite protection) of retained permethrin over the lifetime of the uniform.; (b) Determined the bite protection level of Air Force Battle Uniforms (ABUs) treated with Individual Dynamic Absorption (IDA) kits. The ABUs are a 50/50 nylon/cotton construction similar to Marine Corps Combat Utility Uniforms (MCCUUs); however, unlike MCCUUs, the blouse and trouser weights of ABUs are the same, and the ABUs do not contain a permanent press finish. The IDA kit treatment of ABUs provided > 85% protection against mosquitoes up to 50 standardized wash cycles. (c) Determined the bite protection level of U.S. Marine Corps Fire-Resistant Organization Gear (FROG). The sleeve portion of the FROG provided > 87% protection to 50 standardized wash cycles. The torso portion has very high air permeability due to larger interces in the fabric. It still demonstrated bite protection (50%) out to 50 wash cycles; however, this lower bite protection level is not seen as a sufficient weakness because this area of fabric is intended to be covered by outer layer of body armor under typical circumstances.

3. Pesticide-induced gene expression. Using molecular techniques, 18 different genes were isolated from a pesticide(permethrin)-treated vs acetone-treated Aedes aegypti library. Analysis revealed that 8 of the 18 genes’ expression levels in permethrin-treated Ae. aegypti were at least 2-fold higher than that in acetone-treated Ae. aegypti. These 8 genes include 3 functionally known genes, 3 functionally unknown genes and 2 novel genes. Expression levels for 11 of the 18 genes were induced significantly higher by permethrin than by another pesticide fipronil. Results suggest that molecular methods are powerful techniques to identify differentially expressed genes in response to pesticide treatment. Eight of these genes can now be targeted using newly developed technology to silence genes (RNA interference) for resistance management and/or toxicity.

4. Evaluation of excito-repellency compounds for control of mosquitoes. Resting mosquitoes are poorly controlled by application of aerial pesticide droplets. The addition of compounds to insecticide sprays to activate mosquitoes into flight and enhance mortality was examined in a laboratory wind tunnel. Prallethrin was found to increase the speed and duration of flight, resulted in more droplet deposition and thus, higher mortality. Results from this approach provide the basis for refined mixtures of compounds to activate and kill mosquitoes.

5. Insecticide-treated targets for house fly exclusion. In a test-of-concept evaluation, a perimeter of 26 imidacloprid-treated visual targets was placed around a calf barn with a history of fly invasion from surrounding breeding sites. Targets were switched “on” and “off” each week by covering and uncovering them on alternate weeks for 10 weeks during the fly season. Scudder grid counts indicated a significant reduction in the numbers of flies entering the calf barn when treated targets were in operation. In other developments, a new visual target design was developed that was fully collapsible for ease of transport and deployment. The new collapsible design was as effective as the original model, which relies on a wire skeleton.

6. Salivary gland hypertrophy virus of house flies. Salivary gland hypertrophy virus (SGHV) belongs to a novel group of viruses that infect salivary glands and block egg production in their hosts. During this rating period, a field survey demonstrated that this virus was widely distributed in fly populations on Danish dairy farms, with maximum infection rates of ca. 10%. Transmission studies indicated that the virus was specific to house flies: no infections were found in other sympatric flies (e.g., Scatophaga stercoraria, stable fly, face fly, blow flies, Eristalis tenax) that were injected with SGHV. Danish virus isolates had somewhat higher virulence in lab bioassays than the standard Florida SGHV strain. Transmission tests also demonstrated that virus particles are stored in the crop of the fly and the live virus is deposited in regurgitated material and fecal spots. These results, along with previous studies on surface treatments, suggest that the most effective method for deploying the virus as an operational control tool may be treatment of fly resting sites.

7. Laboratory comparison attraction-inhibitors against Phelebotomus papatasi sand flies in Egypt. A single tube olfactometer was used to evaluate the inhibition of three inhibitors formulated in nanoclays. The nanoclay formulation is designed to release chemical at a constant rate over a 24-hour period. Small vials containing these nanoclays were tested by combining the released chemical in air with odors from the human hand. The reduction in P. papatasi host-finding capability was measured relative to odors from the other hand of the same volunteer. This research demonstrated clearly that all three chemicals suppress host-seeking behavior, similar to results achieved when tested with mosquitoes.

8. Development of a protocol for evaluation of toxicity and spatial repellency actions of candidate chemicals against mosquitoes and flies. There is a need to evaluate the potential of chemical compounds to interrupt vector-host contact. Past efforts have focused only on the toxicity of candidate compounds. Spatial repellency (i.e., the oriented movement of vectors away from a chemical without making tarsal contact with chemical residue) has been ignored because it is difficult to evaluate. A technique was developed which allows both the toxicity and spatial repellency actions of a chemical to be evaluated under semi-field and field conditions. The ability to quantify these chemical actions and the behavioral responses of vector species to these actions is critical for the development of innovative vector control strategies.

9. Reduction of host-seeking responses of mosquitoes by sub-lethal pesticide exposure. Application of pesticides for mosquito control results in direct mortality of those individuals receiving a lethal dose but also a sub-lethal dose for those that only receive a partial treatment. The impact of the sub-lethal pesticide exposure on subsequent host-seeking and subsequent disease transmission is poorly understood. Mosquitoes from three genera were exposed to type 1 and type 2 pyrethroid insecticides. An electrophysiological assay was developed to compare the effects of sub-lethal exposure to permethrin and deltamethrin on sensory responses to several host-attractant compounds. Additionally, a wind tunnel assay was developed to study the behavioral impact on flight orientation to host odors after pesticide exposure. Preliminary results indicated differences between mosquito species and reduced flight after exposure to sub-lethal doses. Results from this study provide the basis for refinement and optimization of pesticide application methodology.

10. Toxicity of carboxamides for adult mosquitoes. The toxicities of 33 pesticides (carboxamides) were evaluated against female Aedes aegypti by topical application. The most toxic compounds of the 33 carboxamides tested had an LD50 (50% lethal dose) value of 0.4 g per mosquito and LD95 (95% lethal dose) value of 1.82 g per mosquito. The least toxic compound had LD50 and LD95 values of 15.66 g and 72.07 g per mosquito, respectively. Each of the nine different categories of carboxamides showed different toxicities against female Ae. aegypti. Structure-activity analysis of the 33 carboxamides may be useful in guiding further carboxamide modifications for the development of potential new insecticides.

11. Change in stable fly target size. Blue-black cloth targets impregnated with 0.1% -cyhalothrin have been shown to be efficacious in preliminary trials as an “Attract-and-Kill” device for stable fly management. The flat targets were formed into cylinders, which made them significantly more stable under high winds, but did not reduce their efficacy. To make the targets more convenient for use, the cylinder size was reduced to 30 cm high x 20 cm in diameter. Reducing the target size yielded a smaller number of flies captured, but more flies per unit area of target were killed. This smaller target can be used by producers to kill stable flies in situations where no other method is suitable.

12. Development of international guidelines for insecticides and repellents. At the invitation of the Director of the World Health Organization (WHO) Pesticide Evaluation Scheme (WHOPES), MFRU scientists played leadership roles with other international experts in the development of WHO Guidelines for: (1) Efficacy Testing of Mosquito Repellents for Human Skin; (2) Efficacy Testing of Insecticides for Indoor and Outdoor, Ground-applied Space Spray Applications; and (3) Efficacy Testing of Household Insecticide Products.

13. Ultraviolet light traps for indoor house fly management are basically an attractant (the light) and a housing. Although there are many types of ultraviolet light traps for house fly suppression, most traps have a housing to hold the fluorescent tubes and the killing or capture device, plus the ultraviolet fluorescent tubes themselves. It is desirable to reduce the amount of light being emitted by the housing so traps will be less conspicuous. Studies at MFRU demonstrated that reducing the visibility of the ultraviolet light by shielding it with perforated covers greatly reduced the numbers of flies captured, sometimes by 50% or more. Based on these results, traps emitting the maximum output of ultraviolet light directly into the environment are most efficacious.

6.Technology Transfer

Number of Active CRADAs1
Number of the New/Active MTAs (providing only)1
Number of Invention Disclosures Submitted1

Review Publications
Amoo, A.O.J., Xue, R.-D., Qualls, W.A., Quinn, B.P., Bernier, U.R. 2008. Residual efficacy of field-applied permethrin, d-phenothrin, and resmethrin on plant foliage against adult mosquitoes. Journal of the American Mosquito Control Association. 24(4):543-549.

Clark, G.G.; Rubio-Palis, Y. 2008. Mosquito vector control and biology in Latin America - an 18th symposium. Journal of the American Mosquito Control Association. 24(4):571-582.

Xue, R.-D., Pridgeon, J.W., Becnel, J.J., Ali, A. 2009. Fipronil as a larvicide against the container inhabiting mosquito, Aedes albopictus. Journal of the American Mosquito Control Association. 25(2):224-227.

Pridgeon, Y.W., Becnel, J.J., Clark, G.G., Linthicum, K. 2009. A High Throughput Screening Method to Identify Potential Pesticides for Mosquito Control. Journal of Medical Entomology 46(2):335-341.

Lietze, V.-U., Sims, K.R., Salem, T.Z., Geden, C.J., Boucias, D.G. 2009. Transmission of MdSGHV among adult house flies, Musca domesitca (Diptera: Muscidae), occurs via oral secretions and excreta. Journal of Invertebrate Pathology. 101:49-55.

Last Modified: 4/25/2014
Footer Content Back to Top of Page