Location: Mosquito and Fly Research
2018 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
Studies with wild and potted flowers are continuing in both the laboratory and field. The phenology studies have shown that over the course of a season mosquitoes and other biting arthropods have access to specific flowering plants for a limited time only. Other possible limitations on the availability of nectar sources are the diel pattern of nectar production of the flowering plants; if biting arthropod diel activity must be synchronized with the plant’s nectar production. The shape of the flower can also affect accessibility to the nectar.
Studies on the discovery and development of new tropical repellents continue in the laboratory.
ARS has screened more than 100 compounds from collaborators during FY2018 against both susceptible and pyrethroid resistant colonies of mosquitoes to identify new active agents. This information has resulted in 3 publications. As part of a collaborative effort with the state of Florida and stakeholders, we characterized the permethrin resistance status of 21 strains of Aedes mosquitoes collected from peninsular FL locations. We also performed genetic analysis to identify insecticide resistance markers from 62 populations. Results showed all strains of Aedes aegypti were resistant although the strength of the resistance varied. In contrast, Aedes albopictus strains were not resistant to permethrin. This resistance information will be utilized by public health officials and control operations. An effective dsRNA construct in Ae. aegypti that targets fecundity has been patented. Current efforts continue to focus 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. This research also led to the identification of a gene that when silenced with a dsRNA trigger results in long-term reductions in reproduction of the house fly. This study demonstrates that gene silencing using dsRNA can be specifically effective and has potential efficacy as a control intervention in adult house flies.
ARS conducted bite protection studies on a variety of permethrin- and etofenprox-treated U.S. military combat uniform fabrics. Changes in fabric construction were evaluated under a value engineering change proposal (VECP). Permethrin treated fabrics under the VECP program all provided bite protection levels of 85% or better from 0 to 50 wash cycles. Etofenprox-treated lightweight fabrics were evaluated and determined to have bite protection levels of 95% or greater at 75 wash cycles. Initial tests were conducted with the first fabrics received from a new jungle warfare uniform was evaluated for bite protection; the bite protection of the fabric at 0 wash cycles was found to be just below the acceptable threshold of 85% and therefore further optimization is needed.
Arrays of novel passive spatial delivery devices are being developed and evaluated. The current objective is to develop this array of devices that can be used to protect individual humans and/or animals from mosquito and other biting fly nuisance, or groups of people or animals located within structures (e.g. tents, stalls) or within defined areas (e.g. military forward operating bases, or livestock feeding areas).
Targets consisting of various types of fabric treated with insecticide are currently being evaluated in semi-field and field situations against mosquitoes and other biting flies. Some of the targets utilize physical and and/or chemical attractants to lure target species to land on the target which results in their death.
Evaluations of final air curtain designs are being conduct with industry partners but further development will depend on the interest of WHO to accept air curtains as an alternate means for aircraft disinsection.
We conducted a series of novel field trials to investigate the residual capability of four larvicide formulations in three distinct environments, hot-humid tropical, hot-arid desert, and warm-temperate Mediterranean, against key medically-important Aedes and Anopheles species mosquito vectors, resulting in 3 publications. We investigated the capability of a new spatial repellent/toxicant to reduce mosquito and sand fly populations in hot-humid tropical, hot-arid desert, warm sub-tropical, and warm-temperate Mediterranean environments. We developed with university and mosquito control district collaborators an unprecedented system to reduce human-biting populations of Aedes aegypti in north Florida through releases of sterilized colony-reared male mosquitoes.
Addition of traps in 3 x 3 Latin square designs in natural field sites are needed to further clarify results collected at present.
With university collaborators from Kansas and Uganda we adapted a model developed to predict Rift Valley fever epidemiology in the U.S. to investigate outcomes of Rift Valley fever infections across cattle operations in a key district of Uganda where existing climate-based models of RVFV spread may not be applicable. We digitized over 60 years of mosquito surveillance data from two important ecological regions of the U.S. for groundbreaking predictive analysis of climate and mosquito populations. We designed a novel analysis to relate changes in disease vector Phlebotomus sand fly populations from long-term longitudinal surveys to changes in landscape-level environmental conditions. We forecasted and issued early warnings to WHO, FAO, and OIE for elevated risk of Rift Valley fever outbreaks which subsequently occurred in 4 African countries (Sudan, South Africa, Kenya, and Rwanda) using global climate data with NASA and DoD partners.
Accomplishments
1. Pyrethroid resistance in Aedes aegypti in Florida is widespread. Recent outbreaks of locally transmitted dengue and Zika viruses in Florida have placed more emphasis on the importance of integrated vector management plans for Ae. aegypti and Ae. albopictus. ARS researchers at Gainesville, Florida, together with collaborators conducted statewide examination of pyrethroid resistance in Florida Ae. aegypti populations and demonstrated that permethrin resistance and the genetic markers for resistance are widely present. Results showed all strains of Ae. aegypti were resistant although the strength of the resistance varied. In contrast, Ae. albopictus strains were not resistant to permethrin. This resistance information will be useful for improved mosquito control operations.
2. Reduction in Musca domestica fecundity by dsRNA-mediated gene knockdown. The house fly (Musca domestica) is a major pest of humans and animals throughout the world. ARS researchers at Gainesville, Florida, and collaborators have identified a gene that when silenced with a dsRNA trigger results in long-term reductions in reproduction of the house fly. This study demonstrates that exogenous dsRNA is specifically effective and has potential efficacy as a control intervention in adult house flies. Further work is required to develop effective methods for delivery of dsRNA to adult flies. This study was published in PLoS ONE.
3. New control method for Aedes aegypti patented. ARS researchers at Gainesville, Florida, and collaborators have identified two dsRNA triggers that cause long-term reductions in reproduction of the Yellow Fever mosquito, Aedes aegypti. The effects of these triggers were expanded and confirmed with several methods. Both triggers target the ribosome which is involved in most cellular systems. Targeting of these genes as a method for control of insects was patented as: Estep, A. S., Sanscrainte, N. D., & Becnel, J. J. Double-stranded ribonucleic acid as control against insects. Issued October 24, 2017.Patent # 9,796,975.
4. Residual larvicide pre-treatment effective against Aedes aegypti across multiple environments. The Aedes aegypti mosquito is a key vector of prominent viruses including dengue, chikungunya, and Zika and is very difficult to control. ARS researchers at Gainesville, Florida, and U.S. and international collaborators demonstrated the efficacy of four common larvicides applied as a residual to dry containers that would later be flooded with water. Studies were conducted across a range of environments relevant to the global spread of this mosquito. Results indicate that pre-treatment of dry habitat vulnerable to flooding can extend the impact of mosquito control agencies that otherwise must treat flooded areas cyclically or in response to mosquito populations that are already developing. These studies were published as a series of papers in the Journal of the American Mosquito Control Association [see references in list at end].
5. Spatial repellents on military materials effective against mosquitoes and sand flies in the field in multiple environments. Military materials commonly used in the field are important substrates for residual pesticides that may protect troops and other personnel from nuisance and disease-vector biting insects. ARS researchers at Gainesville, Florida, and U.S. and international collaborators demonstrated that two types of camouflage netting and one type of material used to retain fill in blast-protection walls can be effectively treated with the spatial repellent/toxicant transfluthrin. Strips of these materials treated with transfluthrin greatly reduce or eliminate populations of both mosquitoes and sand flies in small 1—3 m diameter protected spaces across a range of militarily-relevant environments including tropical, desert, temperate, and Mediterranean. Importantly, strips are easily transported and attached to existing camouflage net or blast-protection structures by minimally trained personnel, creating a rapid shelter from biting insects without having to wait for intervention by mosquito and vector control units.
6. Sterilized male Aedes aegypti from Florida populations survive and exhibit pre-mating behavior in the field. The Aedes aegypti mosquito is a key vector of prominent viruses including dengue, chikungunya, and Zika and is very difficult to control. However, ARS researchers at Gainesville, Florida, and university and mosquito control district collaborators developed a method to sterilize male Aedes aegypti mosquitoes and release them in large numbers to overwhelm wild populations of fertile males. The success of this method depends on sterilized males not only surviving in the wild, but also exhibiting mating behavior competitive with local, wild males such that wild females mate more often with sterilized males. Mark-release-recapture trials in the field with sterilized males produced satisfactory recapture rates, indicating survival in the wild, and led to direct observations of marked males in mating swarms potentially attractive to local wild female Aedes aegypti and the opportunity for subsequent population suppression.
7. Prediction and early warning for elevated risk from Rift Valley fever in Africa. Rift Valley fever is a mosquito transmitted virus that causes a serious and often fatal disease in cattle, sheep, goats, and humans in Africa and the Middle East, with the potential for spread to animals, humans, and mosquitoes in the U.S. and other parts of the world. ARS researchers at Gainesville, Florida, forecasted and issued early warnings to WHO, FAO, and OIE for elevated risk of Rift Valley fever outbreaks which subsequently occurred in 4 African countries (Sudan, South Africa, Kenya, and Rwanda) by analyzing global climate data with NASA and DoD partners. The success of these forecasts resulted in increased surveillance and control efforts in affected countries, minimizing the impact of the disease in local populations of animals and humans and greatly reducing the risk that the disease would be spread to the U.S. and other locations in the world.
Review Publications
Hajek, A.E., Solter, L.F., Maddox, J.V., Huang, W., Estep, A.S., Krawcyzk, G., Weber, D.C., Hoelmer, K.A., Sanscrainte, N.D., Becnel, J.J. 2017. Nosema maddoxi sp. nov. (Microsporidia, Nosematidae), a widespread pathogen of the green stink bug Chinavia hilaris (Say) and the brown marmorated stink bug Halyomorpha halys (Stål). Journal of Eukaryotic Microbiology. https://doi.org/10.1111/jeu.12475.
Tok, F., Kocyigit-Kaymakciogl, B., Tabanca, N., Estep, A.S., Gross, A.D., Geldenhuys, W., Becnel, J.J., Bloomquist, J.R. 2017. Synthesis and structure-activity relationships of carbohydrazides and 1,3,4-oxadiazole derivatives bearing imidazolidine moiety against the yellow fever and dengue vector, Aedes aegypti. Pest Management Science. 74:413–421.
Smith, D.R., Sprague, T.R., Hollidage, B.S., Valdez, S.M., Padilla, S.L., Bellanca, S.A., Golden, J.W., Coyne, S.R., Kulesh, D.A., Haddow, A.D., Koehler, J.W., Gromowski, G.D., Jarman, R.G., Alera, M.P., Yoon, I., Buathong, R., Lowen, R.G., Kane, C.D., Minogue, T.D., Bavari, S., Tesh, R.B., Weaver, S.C., Linthicum, K., Pitt, M.L., Nasar, F. 2018. African and Asian Zika virus isolates display phenotypic differences both in vitro and in vivo. American Journal of Tropical Medicine and Hygiene. 98(2):432-444. doi:10.4269/ajtmh.17-0685.
Altintop, M.D., Tabanca, N., Becnel, J.J., Bloomquist, J.J., Kaplancikli, Z.A., Özdemir, A. 2018. Synthesis and mosquitocidal activity of a series of hydrazone derivatives against Aedes aegypti. Letters in Drug Design & Discovery. https://doi.org/10.2174/1570180814666171002155548.
El-Gamal, A., Al-Massarani, S., Fawzy, G., Atai, H., Al-Rehaily, A., Basudan, O., Abdel-Kader, M., Tabanca, N., Becnel, J.J. 2017. Chemical composition of Buddleja polystachya aerial parts and its bioactivity against Aedes aegypti. Natural Product Research. doi:10.1080/14786419.2017.1378213.
Masi, M., Cimmino, A., Tabanca, N., Becnel, J.J., Bloomquist, J.R., Evidente, A. 2017. A survey of bacterial, fungal and plant metabolites against Aedes aegypti (Diptera: Culicidae), the vector of yellow and dengue fevers and Zika virus. Open Chemistry. 15:156-166.
Meepagala, K.M., Estep, A.S., Clausen, B.M., Becnel, J.J. 2018. Mosquitocidal activity of a naturally occurring isochroman and synthetic analogs from the plant pathogenic fungus, Diaporthe eres against Aedes aegypti (Diptera: Culicidae). Journal of Medical Entomology. 55(4):969–974. doi:10.1093/jme/tjy016.
Sanscrainte, N.D., Arimoto, H., Waits, C.M., Li, L.Y., Johnson, D.M., Geden, C.J., Becnel, J.J., Estep, A.S. 2018. Reduction in Musca domestica fecundity by dsRNA-mediated gene knockdown. PLoS One. 13(1):e0187353. doi:10.1371/journal.pone.0187353.
Waits, C.M., Fulcher, A., Louton, J.E., Richardson, A.G., Becnel, J.J., Xue, R., Estep, A.S. 2017. A comparative analysis of resistance testing methods in Aedes albopictus (Diptera: Culicidae) from St. Johns County, Florida. Florida Entomologist. 100(3):571-577.
Kline, D.L., Hogsette, Jr, J.A., Rutz, D.A. 2018. A comparison of the Nzi, Horse Pal and Bite-Lite H-traps and selected baits for the collection of adult Tabanidae in Florida and North Carolina. Journal of Vector Ecology. 43(1):63-70. doi:10.1111/jvec.12284.
Estep, A.S., Sanscrainte, N.D., Waits, C.M., Louton, J.E., Becnel, J.J. 2017. Resistance status and resistance mechanisms in a strain of Aedes aegypti (Diptera: Culicidae) from Puerto Rico. Journal of Medical Entomology. 54(6):1643-1648. doi:10.1093/jme/tjx143.
Wang, M., Shen, S., Wang, H., Becnel, J.J., Vlak, J.M. 2017. Deltabaculoviruses encode a functional type I budded virus envelope fusion protein. Journal of General Virology. 98(4):847-852. doi:10.1099/jgv.0.000745.
Aldridge, R.L., Golden, F.V., Britch, S.C., Blersch, J., Linthicum, K. 2018. Truck mounted Natular 2EC (spinosad) ULV residual treatment in a simulated urban environment to control Aedes aegypti and Aedes albopictus in North Florida. Journal of the American Mosquito Control Association. 34(1):53-57. doi:10.2987/17-6697R.1.
Britch, S.C., Linthicum, K., Aldridge, R.L., Breidenbaugh, M.S., Latham, M.D., Connelly, P.H., Rush, M.J., Remmers, J.L., Kerce, J.D., Silcox, C.A., Arimoto, H., Dooling, C., Doud, C., Justice, K., Knapp, J., Nunn, P., Spatola, D., Torres-Alvarado, P., Turnwall, B., Yans, M. 2018. Aerial ULV control of Aedes aegypti with naled (Dibrom) inside simulated rural village and urban cryptic habitats. PLoS One. 13(1):e0191555. doi:10.1371/journal.pone.0191555.
Britch, S.C., Linthicum, K., Aldridge, R.L., Golden, F.V., Pongsiri, A., Khongtak, P., Ponlawat, A. 2018. Ultra-low volume application of spinosad (Natular 2EC) larvicide as a residual in a tropical environment against Aedes and Anopheles species. Journal of the American Mosquito Control Association. 34(1):58-62. doi:10.2987/17-6692.1.
Golden, F.V., Britch, S.C., Linthicum, K., Aldridge, R.L., Wittie, J., Gutierrez, A., Snelling, M., Henke, J. 2018. Ultra-low volume application of spinosad (Natular 2EC) as a residual in a hot-arid environment against Aedes aegypti. Journal of the American Mosquito Control Association. 34(1):63-66. doi:10.2987/17-6703.1.
Lloyd, A.M., Farooq, M., Estep, A.S., Xue, R., Kline, D.L. 2017. Evaluation of pyriproxyfen dissemination via Aedes albopictus (Skuse) from a point source larvicide application in Northeast Florida. Journal of the American Mosquito Control Association. 33(2):151-155. doi:10.2987/14-6459.1.
