Location: Mosquito and Fly Research
2017 Annual Report
Objectives
1. Discover safe toxicants and behavior-altering chemicals.
1.A. Discover and develop new attractants for mosquitoes and other biting arthropods.
1.B. Discover and develop new topical repellents for mosquitoes and other biting arthropods.
1.C. Discover and develop new toxicants for mosquitoes and other biting arthropods.
1.D. Discover and develop dsRNA molecules for control of mosquitoes and other biting arthropods.
2. Develop and evaluate systems that disrupt arthropod dispersal, biting, host-finding, or survival.
2.A. Evaluate new fabric treatments and optimize existing treatments to provide improved protection from insect bites through military and civilian clothing.
2.B. Evaluate and optimize spatial repellent systems that protect hosts from arthropods in a local area.
2.C. Evaluate new and optimize existing treated targets.
2.D. Evaluate approaches to disinsection of aircraft.
2.E. Evaluate factors that influence the efficacy of aerosol application and residual pesticide barrier applications on natural and artificial materials in various ecological habitats, including assessment of efficacy in future climates based upon climate projection models. Design the best application methods to mitigate changing climate.
3. Improve accuracy and utility of surveillance techniques.
3.A. Evaluate new and optimize existing trapping systems.
3.B. Develop methods and techniques to accurately assess and predict mosquito population density and timing, and to deploy mosquito vector surveillance systems.
Discover and characterize environmental predictors influenced by climate change that measure the risk of disease from pathogens transmitted by mosquitoes.
Approach
A research focus of this plan is the discovery and development of new chemicals that impact arthropods. The discovery of new repellents will allow improved personal protection from topical application to skin (Sub-objective 1.A), or in a local area through release of chemical in dispersion systems (Sub-objective 2.B). The discovery of new toxicants (Sub-objective 1.C) has potential utility in treated clothing (Sub-objective 2.A) and treated targets (Sub-objective 2.C). New dsRNA molecules that function as insecticides (Sub-objective 1.D) provide a safe and novel means of insect control. Research on how environmental factors influence aerosol and residual control strategies will provide a means for more efficient arthropod control (Sub-objective 2.E). Novel attractants (Sub-objective 1.A) will allow more accurate and efficient surveillance when utilized in new and optimized trapping systems (Sub-objective 3.A). Improved surveillance trapping systems (Sub-objective 3.A) and increased accuracy in prediction of local arthropod populations based on surveillance trap studies (Sub-objective 3.B) will improve models for disease risk and enhance the effectiveness of control strategies. A better understanding of the relationship between environmental factors, and in particular climate change, will allow accurate prediction of vector-borne disease risk in a geographic area and thereby, when and where to employ control strategies to reduce debilitating and lethal illnesses in humans and other animals (Objective 4).
Progress Report
Phenology studies of flowering plants near mosquito larvae development sites were continued. Additional plant species were added to the database. Solvent extracts of two promising flower species were collected and will be evaluated for male and female Aedes (Ae.) albopictus mosquito attraction in a laboratory olfactometer. Over 100 candidate repellents synthesized in house as well as submitted by cooperators were evaluated for repellency. No candidates were successfully repellent enough to merit further exploration. The unit screened more than 150 compounds from collaborators during Fiscal Year 2017 against both susceptible and pyrethroid resistant colonies of mosquitoes to identify new insecticide candidates. This information has resulted in 5 publications. As part of a collaborative effort with the state of Florida and stakeholders, we have expanded our evaluation of pyrethroid resistance in Florida mosquitoes. More than 30 geographically distinct strains of Ae. aegypti and Ae. albopictus have been isolated and characterized. A resistant strain of Ae. aegypti from Puerto Rico (PR) has been investigated to determine pesticide susceptibility and identify the resistance mechanisms. Significant resistance was found when the PR strain was exposed to representative pyrethroids, a sodium channel blocker, and a sodium channel blocking inhibitor, all of which interact with the sodium channel. An effective dsRNA construct in Ae. aegypti that targets fecundity has been developed and has been shown to greatly reduce oviposition. Current efforts are focused on delivery of this construct to adult mosquitoes in a sugar bait and involves testing of a variety of “adjuvants” of biological and synthetic origin. A total of 13 different mosquito bite protection studies of treated U.S. military uniform studies were conducted; one is still in progress. The majority of these were part of a U.S. Army Jungle Fabric and Architecture Development Effort (JFADE) that comprises a variety of different fiber blends, fabric constructions and finishes for use in a jungle environment. The uniforms provided high levels of bite protection from mosquitoes out to 50 wash cycles. A wool blend uniform fabric provided less than idea protection. The Army Combat Uniform (ACU) 50/50 nylon/cotton uniform provided 100% protection through 50 wash cycles. The Value Engineering Change Proposal (VECP) uniforms that were evaluated provided lower bite protection levels than current specifications for the Fire-Resistant Army Combat Uniform (FRACU). Semi-field efficacy studies of prototype devices were conducted under semi-field conditions and a manuscript is in preparation. Prototype designs of slow release insecticide-treated targets were developed and evaluated against three species of laboratory reared mosquitoes under laboratory and semi-field conditions. These studies are still in progress. Discussions with International Civil Aviation Organization personnel and Mechanical Disinsection committee focused upon vector management at airports and how to proceed policy-wise with World Heath Organization on acceptance of mechanical disinsection. Survey to develop airport vector model sent out and discussions will continue. Latin squares of 3 x 3 and 6 x 6 were evaluated semi-field and field studies against laboratory reared mosquitoes and against natural populations. Evaluated new trap designs developed in house and from collaborative studies with the Department of Defense and private industry. Multiple repeated trials were conducted in hot-arid and hot-humid environments with permethrin- and botanical-based misting pesticides against disease-vector mosquitoes. Significant reductions in natural populations of target insects occurred in both environments. Additive, persistent residual effect of both permethrin- and permethrin-based misting formulations on two types of military field materials in both environments were confirmed in laboratory bioassays against a range of target insects. Repeated testing of botanical-based misting pesticides in hot-humid environment indicated effective reduction of natural disease-vector mosquitoes in both wet season and dry season habitat. Preliminary data from pyrethroid residual pesticides on two types of military material in new warm temperate site indicate sustained efficacy for weeks to months post-application against natural populations of both mosquito and sand fly disease-vector insects, and efficacy in laboratory bioassays against a range of target insects. Collaborative studies in warm temperate/subtropical region were initiated to expand residual efficacy study to include military materials subjected to additional weathering due to presence of soil adjacent to treated material, and to investigate efficacy of spatial repellent/toxicant applied to military material. Rift Valley fever risk estimation system was further developed to investigate direct contribution of rainfall to observed Rift Valley fever human and livestock cases in endemic regions. Unique worldwide environmental patterns from unusually large 2015/2016 El Niño event were used to forecast and prevent a Rift Valley fever outbreak in East Africa and were leveraged to refine capabilities to predict disease outbreak clusters of a range of mosquito-borne, water-borne, and rodent-borne diseases including Rift Valley fever, dengue, chikungunya, West Nile fever, cholera, hantavirus, and plague. Sand fly population surveillance data from diverse sentinel sites in East Africa were spatially and temporally analyzed for the first time to determine optimal key locations for future planned longitudinal collaborative study to investigate environmental drivers of dynamics of medically important sand fly populations.
Accomplishments
1. Development of areawide strategy to reduce populations of Aedes aegypti mosquito vectors of Zika, chikungunya, and dengue viruses in the U.S. ARS researchers at Gainesville, Florida, with university, mosquito and vector control district, and government public health agency collaborators developed a comprehensive areawide integrated vector management (IVM) program incorporating traditional, novel, and emerging technology targeting Aedes (Stegomyia) aegypti mosquitoes in high-risk urban and suburban U.S. habitat. ARS researchers led the development of a program that combined vector control, community engagement, and vector surveillance solutions in a unique, innovative areawide IVM system to reduce the risk of transmission of Zika virus by reducing or eliminating populations of the Aedes aegypti mosquito vector. While not designed to develop new IVM components, the program was configured to coordinate the aggressive mobilization, evaluation, and optimization of a suite of existing traditional, novel, and emerging IVM components; position expert personnel; specifically recruit and leverage public engagement; and incorporate state-of-the-art predictive mosquito surveillance at proven mosquito control agencies in two key U.S. regions. This enhanced IVM system would be directed in a consolidated, intensive, and focused way to rapidly produce impact in initial trial regions, with simultaneous evaluation and adjustment, and transition of the optimized system to three additional key US regions with the expectation of immediate impacts at a higher level. This rapid validation would demonstrate the portability and environmental flexibility of the system, uniquely positioning it for immediate distribution to Zika-endemic regions. This areawide system has not yet been adopted but contributed significantly to development of innovative IVM strategies by U.S. and partner nation agencies at local, national, and international levels.
2. Genetic and enzymatic resistance in Aedes aegypti from San Juan, Puerto Rico. Mosquito vectors are increasingly becoming resistant to commonly used public health pesticides and understating the mechanisms is critical to effective control strategies. ARS researchers at Gainesville, Florida, in collaboration with with researchers from the DoD-Navy Entomology Center of Excellence, Jacksonville, Florida, characterized the insecticide resistance status of a San Juan, Puerto Rico, strain of the Yellow fever mosquito Aedes aegypti. The contribution of both enzymatic detoxification and genetic mutations to the overall resistance profiles were examined for Aedes aegypti collected from San Juan, Puerto Rico. Screening of a panel of toxicants found broad resistance relative to the laboratory susceptible Orlando mosquito strain. We identified significant resistance to representative pyrethroids, a sodium channel blocker, and a sodium channel blocking inhibitor, all of which interact with the sodium channel. Molecular characterization indicated that two common sodium channel mutations were fixed in the population. Topical bioassay with synergist and expression level screening of metabolic enzymes indicated some contribution from enhanced enzymatic detoxification. This represents the first study of Puerto Rican Aedes aegypti to examine the contribution of both genetic changes and enzymatic detoxification in the same strain and highlights the necessity of monitoring for resistance and defining resistance mechanisms to develop effective mosquito control strategies.
3. Investigation of pesticide application strategies to control Zika vectors. ARS researchers at Gainesville, Florida, in partnership with the Florida Army National Guard, the Coachella Mosquito and Vector Control District (California), and the Armed Forces Research Institute of Medical Sciences (Thailand) investigated efficacy of biologically-based liquid larvicide applied as a residual against Aedes mosquito vectors of Zika, chikungunya, yellow fever, and dengue viruses. Operational mosquito control resources are universally limited and may not be present when habitats flood that favor the emergence of Aedes aegypti or Aedes albopictus mosquito vectors. Larvicide applied as a residual to habitats ahead of flooding could increase the efficiency and timeliness of integrated vector management and help reduce risk of virus transmission to humans. This research consists of the first known trials of biologically-based liquid larvicide applied as a residual in key hot-arid, warm-temperate/subtropical, and wet-and dry-season tropical habitats. These trials were designed to determine the relative capability of residual larvicide to reduce survival of Aedes aegypti and Aedes albopictus larvae in sentinel containers placed in naturally vegetated and human dwelling habitats. Results indicated that the residual larvicide could be effective on a gradient determined by relative exposure through vegetation or distance into the human dwelling structure. These field trials demonstrate that effective control of larval Aedes aegypti and Aedes albopictus mosquitoes may be enhanced using existing pesticides applied with novel techniques.
Review Publications
Aldridge, R.L., Kaufman, P.E., Bloomquist, J.R., Gezan, S.A., Linthicum, K. 2016. Impact of topical application site efficacy of permethrin and malathion on Culex quinquefasciatus. Journal of the American Mosquito Control Association. 32(4):300-307.
Aldridge, R.L., Britch, S.C., Allan, S.A., Tsikolia, M., Calix, L.C., Bernier, U.R., Linthicum, K. 2016. Comparison of volatiles and mosquito capture efficacy for three carbohydrate sources in a yeast-fermentation CO2 generator. Journal of the American Mosquito Control Association. 32(4):282-291.
Britch, S.C., Nyberg, H., Aldridge, R.L., Swan, T., Linthicum, K. 2016. Acoustic control of mosquito larvae in artificial drinking water containers. Journal of the Mosquito Control Association. 32(4):341-344.
Bekircan, Ç., Bülbül, U., Güler, H.I., Becnel, J.J. 2016. Description and phylogeny of a new microsporidium from the elm leaf beetle, Xanthogaleruca luteola Muller, 1766 (Coleoptera: Chrysomelidae). Parasitology Research. doi:10.1007/s00436-016-5349-y.
