Location: Mosquito and Fly Research2016 Annual Report
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.
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).
In the second year of phenology studies, species of flowering plants were documented; some species flowered earlier than in previous years and the flowering period did not persist as long as in previous years. Studies on the attraction of Aedes (Ae.) albopictus to flowering plants in suburban settings were completed and it was determined that of the commonly used landscape plants, the butterfly bush (Buddleja davidii) was found to be the most attractive plant in the suburban setting. Olfactometer studies to determine the attractancy of the volatiles emanating from the intact flowers have been delayed due to the olfactometer system not being available due to ongoing repairs. There were 38 compounds tested for repellency against Aedes aegypti mosquitoes. Approximately half of the candidate repellents were synthesized by ARS. Nearly 25% of all repellents tested were efficacious repellents but none exceeded the performance of the DEET standard. Screened approximately 360 compounds during FY 16 in both susceptible and pyrethroid resistant colonies of mosquitoes. As issues of pyrethroid resistance continue to become more pronounced in mosquitoes, we have continued our efforts to screen geographically distinct strains of Ae. aegypti and Ae. albopictus and characterize the resistance patterns. We now have seven strains of resistant Ae. aegypti from Florida and Texas with combinations of resistance mechanisms. A dose response curve has been developed for the current leading dsRNA trigger that targets fecundity in Ae. aegypti. Data show that doses as low as 50 ng/org produced significant effects and that doses greater than 100 ng/org produced maximal activity. This will provide guidance on an effective dosing when initiating dose curves for oral delivery of dsRNA. Six commercially available transfection reagents were evaluated for efficacy in delivery of dsRNA triggers in sugar baits. None of these products improved delivery in Aedes aegypti. We continue to test and evaluate additional delivery methods including silicon carbide nanotubes which have been shown to be effective in mediating nucleic acid uptake by creating small punctures in the gut membrane. The evaluation of permethrin-treated Marine Corps Combat Utility Uniforms (MCCUUs) washed up to 150 times was completed. It was determined that the blouses and trousers prevented 96% or greater bites out to 50 wash cycles. By 100 washes, the blouses still protected at the 90% level and trousers at 70%. The uniform bite protection dropped off further and at 150 wash cycles, bites received through trousers were equal to that of untreated fabric. Spatial repellent devices were tested against mosquitoes and flies in a semi-field environment and found to vary in effectiveness by active ingredient, concentration, delivery device, environmental conditions, and target species. Collaborative studies were initiated with the Department of Material Science and Engineering to optimize material and application rates of essential oils, candidate anosmic compounds, and volatile pyrethroid compounds in semi-field studies against laboratory reared mosquitoes utilizing baited traps as surrogate hosts. Plans to compare efficacy of these devices against these traps versus live human hosts were delayed due to the lack of an approved IRB to conduct these studies. Interagency discussions have led to possible interest in using mechanical disinsection of aircraft in the future. Extensive trials were conducted in hot-arid and hot-humid environments with botanical-based misting pesticides against filth-breeding flies and disease-vector mosquitoes. Reductions in natural populations of both target insects were observed in both environments. Investigations of additive residual effect of both botanical-based and permethrin-based misting formulations on two types of military field materials were initiated. Preliminary data from laboratory bioassays against a range of target insects suggest that both misting formulations provide persistent residual insecticidal properties on these materials. U.S. Rift Valley fever risk estimation system development update. Extensive analysis of long-term mosquito field surveillance data was incorporated into an advanced network analysis model to investigate potential outcomes of standard mitigation measures to contain an outbreak of mosquito-borne Rift Valley fever in U.S. cattle. Model simulations demonstrated an interplay between a range of disease transmission capabilities of a variety of mosquito species and the connectivity among cattle operations, such that disease transmission can be widespread even with less-capable mosquitoes if connectivity is high. Trap studies determined that “One-Size-Does-Not-Fit-All”. Many factors were evaluated such as trap color, size, shape, orientation and use of physical and chemical attractants. By selecting a certain combination of these factors a targeted species or group of species can be captured without impacting other species in the geographical study area. This information may be used to capture specific species involved with the transmission of disease pathogens. Collaborative molecular studies of the salivary proteins of Ae. aegypti were conducted with the College of Medicine, University of Central Florida, to isolate unique proteins to create aptamers that can be incorporated into a passive device with known attractants to detect the presence and abundance of this species in a given geographic area without the need to capture the specimen in a trap.
1. Evaluation of pesticide application strategies to control Zika vectors. ARS researchers from Gainesville, Florida, in partnership with the Florida Army National Guard investigated efficacy of liquid larvicide against mosquito vectors of Zika, chikungunya, yellow fever, and dengue viruses. The relative capability of sprays of EPA-approved larvicides to penetrate into buildings or through vegetation where medically important mosquitoes may develop is not well known. ARS researchers conducted first known comparative studies of spray applications of biologically-based liquid larvicide targeting Aedes aegypti and Aedes albopictus in a simulated urban environment in Florida, hot-arid desert environment in California, and dry-season tropical environment in Thailand. These three locations represent environments where Aedes aegypti and Aedes albopictus may currently be found in the U.S. and abroad. Studies were designed to evaluate the capability of the larvicide spray to penetrate mosquito breeding areas hidden in outdoor vegetation or located within simulated residences. Results indicate poor penetration into buildings or vegetation in all three environments, even at point-blank range. Similar tests in Thailand against other medically-important mosquito species besides Aedes aegypti and Aedes albopictus showed moderate to good efficacy. These field trials demonstrate that effective control of larval Aedes aegypti and Aedes albopictus mosquitoes may not be possible with traditional methods, and will require specific techniques and formulations not yet tested.
2. Early warning system introduction of Rift Valley Fever into the United States. ARS researcher from Gainesville, Florida, evaluated outcome of Rift Valley fever early warning system in affected regions of the Horn of Africa. Few opportunities exist to validate nor evaluate mitigations resulting from the time-specific and geographically-specific warnings of a computer simulation model designed to highlight areas at elevated risk of transmission of Rift Valley fever, a devastating mosquito-borne disease of livestock and humans, because outbreaks of the disease occur cyclically nearly by the decade. Traveled to endemic African regions flagged November, 2015, to March, 2016, for potential Rift Valley fever disease activity by the joint USDA-ARS-CMAVE, NASA-GSFC, and DoD Armed Forces Health Surveillance Center effort to monitor outbreaks of the disease based on key environmental signals (http://www.ars.usda.gov/Business/Docs.htm?docid=23464). The flagged regions were evaluated for presence of Rift Valley fever outbreaks and/or Rift Valley fever virus mitigation activities, and it was determined that the alerts produced by the outbreak warning system compelled the government of Kenya to conduct a mass vaccination of domestic livestock, possibly averting a major outbreak of the disease.
3. Gene silencing technology for mosquito control. There are a very limited number of public health pesticides available for controlling medically important vectors, such as mosquitoes and sand flies. This novel approach is based on the technology that allows for the specific silencing of genes critical to survival of the target vector species. This technology uses double stranded RNA (dsRNA) and the process of RNA interference (RNAi) to selectively silence gene products (proteins) that debilitate the mosquito vector and prevent disease transmission. ARS scientists and collaborators in Gainesville, Florida, have demonstrated that dsRNA targeting transcripts of ribosomal proteins (RPS6 and RPL26) reduced fecundity more than 88% in Ae. aegypti for the first oviposition cycle. Reduced fecundity continued through a second oviposition cycle, more strongly for dsRPS6, indicating a lengthy effective period from one treatment. Dissections at 36 hours post-blood meal indicated defects in oocyte provisioning. Further studies with dsRPS6 indicate a dose response effect with maximal reduction in fecundity at 200ng/org. Reduction of gene expression was present in the ovaries but was most pronounced in the abdomen. These studies indicate that target selection, dsRNA format, dose, and tissue susceptibility are critical parameters that must be considered for development of effective RNA based pesticides to control mosquito vectors.
4. Models to predict the spread of Rift Valley Fever disease. ARS researchers from Gainesville, Florida, with Kansas State University collaborators developed a new application of long-term surveillance data of medically important U.S. mosquito populations for disease spread modeling. Computer simulation models that attempt to predict patterns of spread of Rift Valley fever, a devastating mosquito-borne disease of livestock and humans, in the U.S. are limited by excessive assumptions and estimations of mosquito vector and vertebrate host population dynamics. Multi-decade record of medically-important mosquito population dynamics in Fort Riley, Kansas, was used for the first time to estimate the capacity of potential U.S. mosquito vectors of Rift Valley fever virus to spread the virus among cattle farm operations in a network model. This model generated specific outcomes of disease spread under real-world scenarios and revealed that even if mosquitos poorly transmit the virus there can be widespread outbreaks if the disease is not recognized in time to restrict movement of cattle among farms, sale barns, and feedlots. This model may be used to evaluate and optimize real-world emergency mosquito control and cattle movement restriction response measures in the event of an introduction of Rift Valley fever virus into U.S. cattle-producing areas.
5. Mosquito bite protection of permethrin-treated U.S. Marine Corps Combat Utility Uniforms (MCCUUs) washed up to 150 times. The bite protection of permethrin-treated U.S. military combat uniforms is usually evaluated out to 50 wash cycles. This wash cycle end point was chosen based upon the expected life time of older 100% cotton combat uniforms. The MCCUUs are composed of 50% nylon and 50% cotton and last longer than 50 wash cycles. ARS researchers in Gainesville, Florida, conducted bite protection studies of MCCUU blouse and trouser uniform fabrics, washed up to 150 times. The blouses provided 95% or better bite protection out to 120 wash cycles, while the trousers fell below 95% after 50 wash cycles. These data establish that uniforms remain intact out to 150 wash cycles and in the case of blouses, the treatment is very efficient at preventing bites out to 130 washes for blouses. The trousers still exhibited some protection (35%) in the 130-140 wash range, and fell to 0% at 150 washes. This information will be used by the U.S. Marine Corps to better understand the bite protection provided by permethrin-treated uniforms when the uniforms are washed up to 150 times.
6. Pesticide-treated fabric barriers to reduce biting arthropods. ARS researchers from Gainesville, Florida, in collaboration with international partners deployed pesticide-treated military fabrics in a new, warm temperate environment and expanded existing treated materials studies in a tropical environment. Standard military field materials can be enhanced with pesticide treatments to provide additional protection to troops from disease-carrying and nuisance insects. Conducted first known study demonstrating efficacy of residual pesticides on two key U.S. military field materials, HESCO blast wall geotextile and ULCANS radar-scattering camouflage netting, in a warm temperate environment in Greece to reduce populations of medically important European (Old World) arthropods including day-biting Aedes (dengue, Zika, and chikungunya virus vectors) and night-biting Culex (West Nile virus vectors) mosquitoes and night-biting Phlebotomus (leishmaniasis vector) sand flies. Enhanced field site in Thailand during the rainy season with larger perimeters of HESCO barriers to represent U.S. military field use of HESCOs and conducted trials there with residual pesticides supplemented with pesticide misting systems to effectively reduce populations of medically important Aedes and Anopheles mosquitoes. These studies demonstrate the flexibility of pesticide-treated military materials and pesticide misting systems to be effective in multiple militarily-relevant environments.
7. Acoustic device to kill mosquito larvae. ARS researchers from Gainesville, Florida, in partnership with product developer conducted first known efficacy study of an acoustic larvicide device in 55 gallon stored water containers against mosquito vectors of Zika, chikungunya, yellow fever, and dengue viruses. ARS researchers determined that a 5 second exposure in 50 gallons of water could kill at least 90% of the mosquito larvae present, and that a 9-18 second exposure could kill close to 100%. These results provide key baseline data from which to evaluate non-chemical technology to control immature mosquitoes in water stored for human consumption, which could increase acceptance of integrated vector management programs in developing nations and reduce risk of transmission of mosquito-borne disease to humans.
8. Comprehensive review of Rift Valley Fever and vectors of this disease. ARS researchers at Gainesville, Florida, with NASA-Goddard Space Flight Center collaborator published an in-depth review of Rift Valley fever virus entomology and emerging globalization. This unique review of Rift Valley fever virus, a virus that causes devastating mosquito-borne disease of livestock and humans, focuses on the mosquitoes that transmit the disease, their relationship with environmental dynamics, and the capability of the disease to spread outside of its normal range. This publication presents a definitive table of all known arthropod and non-arthropod endemic and emerging vectors of the virus, which provides a distinctive reference for current and ongoing efforts to protect the US from invasion and establishment of Rift Valley fever virus.
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