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United States Department of Agriculture

Agricultural Research Service


Location: Mosquito and Fly Research Unit

2009 Annual Report

1a.Objectives (from AD-416)
1) Identify, and evaluate chemical attractants to augment trap selectivity and efficacy under laboratory and field conditions. 2) Design, develop, and evaluate innovative, robust, automated and economically feasible traps capable of selective sampling of mosquitoes, biting and filth-breeding flies. 3) Investigate relationships between mosquito and fly biology, physiology, and behavior and disease transmission and surveillance. 4) Design and validate automated, remote surveillance systems that incorporate selective trapping and global information technology to direct control efforts.

1b.Approach (from AD-416)
Conduct basic laboratory and field research to determine the relationship(s) between mosquito biology, physiology, and behavior and disease transmission, surveillance, and control. Design, develop, and evaluate innovative, robust and inexpensive traps capable of selective sampling of biting and filth-breeding flies. Isolate, identify, and adapt chemical attractants to augment trap selectivity. Devise accurate biological assays to evaluate attractant activity for biting and filth-breeding flies under laboratory and field conditions. Design and validate surveillance systems based on an understanding of the quantitative relationship between mosquito activity in time and space and the presence/absence of biotic and abiotic factors with GIS technology to predict disease transmission patterns and to direct control efforts.

3.Progress Report
A thorough understanding of the habits of these insects is essential to the development and implementation of control strategies for the protection of livestock and people from mosquitoes and flies that may transmit pathogens. Among the pathogens that they transmit are viruses (e.g., West Nile and Rift Valley fever), bacteria and parasites that cause diseases in animals and humans. One objective of a field research project is to determine which mosquito species are responsible for transmission of West Nile virus to horses and humans. Information is being obtained on many aspects of the target species’ life cycles, such as temporal and spatial information on their breeding, feeding and dispersal patterns. Cues (visual, physical and chemical) that mosquitoes use to locate their hosts and subsequently oviposition sites are under investigation in laboratory, semi-field and field studies. Trap design, placement, various attractant combinations and delivery systems are being evaluated. Trapping, as a means to monitor mosquito populations, is an integral component of surveillance efforts; yet standard techniques for interpreting the results are lacking. Thus, another ongoing project is being conducted to determine trap biases. Knowledge of these biases is essential when deciding what traps to use, where and when to deploy them, and how to interpret the results that they produce. Efforts are being directed toward the use of spatial models to identify high risk areas for mosquito-borne diseases. These models will be used to guide intervention efforts. Understanding the limitations of mosquito surveillance data is necessary to improve the accuracy of these spatial models. Electrophysiological methods (GC-EAD, EAG and single-sensillum recordings) are ongoing for identification of new compounds as host-associated (human and avian) and oviposition attractants for Culex and Aedes mosquitoes. Additionally, the characterization of the impact of known and new repellents and inhibitors on the electrophysiological responses of mosquitoes to host odors is on-going. Evaluations of new lures for Culex mosquitoes containing new compounds and mixtures of compounds developed under laboratory and field conditions were continued. Field studies were initiated of different infusions to determine optimal concentration and source material for attraction of gravid Aedes albopictus. Mixtures of compounds identified from bovine and avian blood that enhance the attraction and landing responses of Aedes aegypti and Culex quinquefasciatus were also continued. Studies were continued of in-flight analysis of orientation of mosquitoes to individual or combinations of chemicals and used to characterize flight paths of Aedes aegypti to avian and human host odors that differ in volatility.

1. Attractants and trap placement for Aedes albopictus. Monitoring for Aedes albopictus is difficult due to the relatively low response of mosquitoes to current traps. Infusions of different plant leaves were compared to determine the most attractive for females ready to oviposit. Infusions of oak and pine were effective in attracting mosquitoes and these were used to bait traps placed at different heights in wooded areas. Traps placed at ground levels were the most effective. This provides the basis for enhanced mosquito surveillance through optimized placement and lures in these traps.

2. Develop sampling procedures for adult mosquito populations. New and improved methods are needed to obtain accurate estimates of adult mosquito population density for purposes of vector abatement and to prevent disease epidemics. Capture rates of female Aedes albopictus, Anopheles quadrimaculatus, Culex nigripalpus, Culex quinquefasciatus, and Ochlerotatus triseriatus in CDC-type light traps supplemented with CO2 (LT) and using the human landing (HL) collection method were observed in matched-pair experiments and compared for agreement on a catch-per-unit-effort basis using HL as the response comparison baseline. Patterns of activity and mosquito densities indicated by each collection method generally lacked temporal congruency and the mean capture rate efficiency of LT compared with HL was =15% for all species except Cx. quinquefasciatus (43%). Statistical models of the relationship between responses to LT and HL indicate that except for Ae. albopictus LT capture rates can be accurately estimated from the mosquito landing rate on a human subject during specific times of the diel period. Estimates based on observations made between sunset and sunrise were most precise in this regard for An. quadrimaculatus and Cx. nigripalpus as were those between sunrise and sunset for Cx. quinquefasciatus and Oc. triseriatus.

3. Attractants for floodwater mosquitoes. Lures and placement location were tested in studies utilizing Centers for Disease Control (CDC)-type traps in a Latin square design. The study was conducted in a suburban Florida neighborhood located adjacent to a freshwater wetland. Commercial and experimental lures, which contained various blends of compounds that had been isolated from human and other animal host emanations, were used in combination with carbon dioxide. Attractant blend, trap location (distance within or away from wetland) and mosquito species were significant factors affecting trapping efficacy.

4. Develop strategies for the deployment of mosquito traps in vector surveillance systems. Use environmental predictors of mosquito activity in a geographic information system (GIS) to identify ideal locations for the placement of mosquito traps in a vector surveillance system. In this study, historical vector surveillance data (from Chatham County Mosquito Control, Savannah, GA) have been organized into a geodatabase. Land use was classified and Normalized Difference Vegetation Index calculated from a 15m Landsat image. Other ecological elements such as urbanization, proximity to storm sewers, and the age of structures associated with urbanization (e.g. residences, industrial buildings, retention ponds, etc.) in the study region were obtained, quantified, and/or derived and selected locations characterized on the basis of these parameters and vector density. Several variables, including soil type and urbanization-associated factors are correlated with vector activity. These variables are being evaluated in detail for incorporation into a predictive GIS-based model that will enable the placement of mosquito traps in the environment when used in surveillance systems for mosquito vectors.

5. Built upon 2006-2008 foundation of strategic inter-agency partnerships and synthesis of research programs to protect the US against Rift Valley fever (RVF). Rift Valley fever virus (RVFV) is a potential emerging mosquito-borne viral threat that could lead to severe impacts on the economy and public and veterinary health should it emerge in the U.S. Although U.S. agencies and universities are actively creating response/surveillance plans for RVFV and researching critical technological advances such as diagnostics and vaccines, improvements are needed in communication and/or integrated response efforts should RVFV unexpectedly arrive in the U.S. MFRU staff have organized key researchers and administrators from federal and state agencies and universities into the RFV Working Group (RVFWG). The RVFWG continues to have a measurable positive impact on RVF research directions and outcomes, and set a trajectory that will significantly strengthen and protect the US against the possible arrival of RVFV as well as other mosquito-borne viruses currently or potentially impacting the US economy and public and veterinary health. MFRU staff continued work on a second draft of a comprehensive RVFWG White Paper, shared climate data with RVFWG collaborators, were invited as consultants for USDA sponsored area-wide mosquito control plans, hosted a student intern to study population dynamics of potential RVFV mosquito vectors in the U.S., participated in international RVF and NTD meetings in Nairobi, Kenya, Cairo, Egypt, and Cape Town, South Africa, published a landmark article on a successful prediction of the 2006-2007 RVF outbreak in Africa, and offered a short course on RVFV and RVF issues in the US at a national mosquito control meeting.

6. Effect of different attractants on flight characteristics of Aedes mosquitoes. Compounds produced by hosts serve as cues to attract mosquitoes for blood-feeding resulting in annoyance and possibly disease transmission. These compounds are used attractants to enhance traps collections. Flight path characteristics of host-seeking mosquitoes were examined in a wind tunnel to evaluate approach and directness of flight to several attractant compounds. Parameters such as time to flight initiation, duration of flight, duration of flight, directness and altitude of flight differed between compounds. Understanding flight responses to compounds can provide the basis for optimization of attractant used and trap design development for enhanced collection of mosquitoes.

7. Continued accumulation, integration, and analysis of U.S. climate data and U.S. mosquito population surveillance data at the national level. GIS models of climate-population and habitat-population associations to predict temporal and spatial distribution and abundance of medically-important mosquito species are being developed. Products of these models will be key elements of mosquito borne disease risk maps, focusing on potential U.S. mosquito vectors of Rift Valley fever (RVF) virus. Published MFRU studies have shown that U.S. satellite-based climate data are a powerful tool in forecasting high densities of mosquitoes at local, regional, and national levels. MFRU in collaboration with NASA built upon these studies to develop new techniques that showed a combination of satellite and ground-based environmental data at local and regional levels analyzed early in the year may yield reliable warnings of unusually high mosquito densities later in the year. Techniques, only possible with long-term population data, were expanded into detailed analyses of anomalous changes in US populations following hurricane events. A spatially explicit bionomics database is being expanded for quick reference and triage should a mosquito-borne disease emergency strike one or several U.S. regions simultaneously. Integrating these products with MFRU’s African remote-sensing RVF virus prediction model, will lead to an RVF virus early-warning GIS for the US which will target key areas, e.g. ports, for heightened disease surveillance, prevention and response efforts; potentially reducing severity of future exotic mosquito-borne disease outbreaks in this country. The underlying concepts and operational design of this system were keystone contributions to the RVF Interagency Working Group White Paper.

8. Enhanced collections of sand flies with lights and chemical attractants. Commercial mosquito traps (Mosquito Magnet -X and Centers for Disease Control (CDC) light traps) were evaluated with red and near-UV LEDs for collection of Lutzomyia sand flies. Traps were additionally baited with carbon dioxide or a mixture of host attractant compounds. Host attractant compounds in combination with carbon dioxide significantly enhanced collection of sand flies in traps fitted with either light. Both types of lights enhanced overall collections. Improved trapping enhances vector and surveillance efforts.

9. Identification of pollen on stable flies. The strong flying ability of stable flies has made management difficult and methods to determine their origin on farms are still being evaluated. Flies captured at a study site were covered with pollen, which could indicate the route the flies used to reach the study site. The pollen was from willow trees, a common small tree in wetland areas.

Review Publications
Jarzen, D.M., Hogsette, J.A. 2008. Pollen from the exoskeletons of stable flies, Stomoxys calcitrans (Linnaeus 1758), in Gainesville, Florida, U.S.A. Palynology. 32:77-81.

Reinert, J.F. 2008. Comparative anatomy of the female genitalia of generic-level taxa in tribe Aedini (Diptera: Culicidae). Part XXIII. Genus Tanakaius Reinert, Harbach and Kitching. Contributions of the American Entomological Institute. 35(4):1-9.

Reinert, J.F. 2008. Comparative anatomy of the female genitalia of generic-level taxa in tribe Aedini (Diptera: Culicidae). Part XXIV. Genus Vansomerensis Reinert, Harbach and Kitching. Contributions of the American Entomological Institute. 34(4):11-19.

Reinert, J.F. 2008. Comparative anatomy of the female genitalia of generic-level taxa in tribe Aedini (Diptera: Culicidae). Part XXV. Genus Dobrotworskyius Reinert, Harbach and Kitching. Contributions of the American Entomological Institute. 35(4):21-30.

Reinert, J.F. 2008. Comparative anatomy of the female genitalia of generic-level taxa in tribe Aedini (Diptera: Culicidae). Part XXVI. Genus Collessius Reinert, Harbach and Kitching. Contributions of the American entomological Institute. 35(4):31-41.

Linthicum, K. 2008. Insects of war, terror and torture. Nature. 456:36-37.

Obenauer, P.J., Kaufman, P.E., Allan, S.A., Kline, D.L. 2009. Host-seeking height preferences of Aedes albopictus (Diptera: Culicidae) in North Central Florida suburban and sylvatic locales. Journal of Medical Entomology. 46(4):900-908.

Last Modified: 4/16/2014
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