2010 Annual Report
1a.Objectives (from AD-416)
1. Determine components of behavior leading to resource location by Aedes albopictus and Culex pipiens group species/hybrids. Resources to be studied are: resting sites, sugar sources, mates, blood-meal hosts, and oviposition sites.
2. Determine chemical and other cues associated with regulation and orientation of specific behaviors by Aedes albopictus, Culex pipiens group species/hybrids, and Ixodes scapularis that can be applied to the solution of operational surveillance and control problems.
3. Discover and characterize environmental predictors of the distribution of mosquitoes in order to assess the risk of invasive species and pathogen transmission. Apply to the development of methods and techniques to accurately assess mosquito population density, to deploy vector surveillance systems, and to detect exotic invasive species. Discover the current, and estimate the future (with changing climate) of spatial and temporal distribution of the mosquito vectors of vector-borne diseases in the United States.
1b.Approach (from AD-416)
1. Conduct laboratory studies to describe and characterize behavioral steps involved in resource finding by mosquitoes that may facilitate discovery of new approaches for surveillance and control.
2. Determine factors that result in positive resting site selection responses by adult mosquitoes as a basis for optimizing use of natural and artificial shelters for surveillance of mosquitoes. Determine volatile chemical cues associated with mate location through behavioral and chemical studies. Determine cues used for location and utilization of sugar and nectar sources. Using behavioral, chemical and electrophysiological methods, plant-derived compounds that attract mosquitoes will be identified and then evaluated in the field for surveillance. Determine factors that influence host-finding behavior with emphasis on the discovery of new chemical attractants based on host odors. Visual, thermal, and other non-chemical cues enhance host-finding behavioral responses to olfactory cues and these will be evaluated to enhance trap efficiency. Devise strategies for mosquito surveillance that utilize cues from oviposition sites. Using behavioral and chemical analysis, new chemical attractants will be identified and evaluated in the field. Determine cues that regulate behaviors in ticks with specific focus on the role of host odor compounds that may provide attractants for surveillance. Evaluate the effect of toxicant exposure on arthropod behavior through detailed behavioral analysis to better target toxicant impact.
3. Develop methods and techniques to accurately assess mosquito population density through comparison of trapping, resting, and landing collections. Characterize environmental predictors of mosquito distribution in time and space through field sampling and spatio-temporal models to provide strategies for accurate assessment of mosquito populations. Discover and develop ecologic and climatic factors to assess population densities of actual and potential vector mosquitoes in the US, and using Rift Valley fever (RVF) as a model disease system, evaluate the risk of exotic species and disease introduction into the U.S.
4. Identify and evaluate attractants for larval mosquitoes that can be developed and tested in the field to provide new strategies for larval surveillance.
The ultimate goal of this research is to discover, evaluate and incorporate aspects of the sensory ecology of blood-seeking arthropods into useful tools and deployment strategies for surveillance and control. Rift Valley fever virus is an emerging mosquito-borne pathogen that threatens public and veterinary health in the U.S. ARS scientists in Gainesville, FL, with inter-agency collaboration provided a warning of an outbreak in South Africa that resulted in preventative measures likely deterring an outbreak of greater impact in South Africa and the U.S. This approach resulted in the successful predictions of an earlier outbreak to be published in the Proceedings of the National Academy of Sciences. Development of effective attractants can provide the basis for effective surveillance strategies. Commercial lures based on host odors evaluated against the Asian Tiger Mosquito (Ae. albopictus) in the laboratory and field were moderately effective in attraction of this species. Sugar-feeding behavior of mosquitoes can form the basis for development of new attractants which, in turn, can be used for development of lures for trapping. The availability of different flowering plants for sugar-feeding by mosquitoes was characterized over a year. The volatile profiles of 27 plant species were determined as the basis for identification of chemicals that attract mosquitoes to flowers for sugar-feeding. In addition to olfactory cues, visual cues affect mosquito response. The effectiveness of different colors and patterns on cylindrical traps were evaluated against the Asian Tiger Mosquito with traps with horizontal black and white stripes being most effective. Combination of optimal olfactory and visual cues is critical for optimized surveillance against this mosquito species. Optimal placement of traps is critical for effective surveillance and in a study on accuracy of assessment of different methods for mosquito collection, 80% of the species collected were in light trap samples and 30% in suction traps or landing collections. Species differed in their abundance and presence between trapping methods. Collection of resting mosquitoes is under-utilized for surveillance and in a field study on resting site locations, resting Culex were located near refugia such as tree stumps and exposed root systems. Light intensity and surface temperature appeared to influence presence of Culex. Development of a larval mosquito attraction assay provides the basis for studies on chemical and visual cues that could form the basis for development of a standardized larval surveillance method. Sublethal exposure of three species of mosquitoes to pyrethroid insecticides resulted in altered flight behavior and lower responses to attractants.
Developed methods and techniques to accurately assess mosquito population density. Samples of the adult (female) mosquito population in a Florida swamp (Sumter County) were obtained by ARS scientists in Gainesville, FL, using suction traps and portable Center for Disease Control (CDC) light traps (augmented with CO2) and the results compared with mosquitoes captured by mechanical aspirator when landing on a human subject. Sixteen mosquito species in the genera Aedes, Anopheles, Coquilleittidia, Culex, Culiseta, Mansonia, and Psorophora were collected in preliminary studies. Eighty percent of these species were observed in light trap samples and 30% each in suction trap samples and in collections of landing mosquitoes. All of the species obtained by suction trap were represented in the light trap samples although the relative abundance of each species in light and suction trap samples differed significantly. Three of the five mosquito species collected from human subject were not obtained in light trap or suction trap samples.
Olfactometer/semi-field evaluations of host-associated odors against the Asian Tiger Mosquito. Chemical compounds previously identified as host-finding attractants for other mosquito species were evaluated against the Asian Tiger Mosquito in laboratory olfactometer and semi-field studies by ARS scientists in Gainesville, FL. Several commercially available lures were moderately effective in attracting this species; others required the addition of carbon dioxide to be effective. Improved attractant lures based on host odors are needed for this mosquito species. These studies will aid in the commercial development of improved host associated lures.
The sublethal affects of pesticides on mosquito host-seeking behavior. Control efforts against adult mosquitoes primarily consists of aerial spraying and residual barrier treatments, often using neurotoxic pyrethroids. However, not all mosquitoes contact a lethal dose of insecticide and the effect of sublethal exposure to these neurotoxic insecticides on sensory organs is poorly characterized. ARS scientists in Gainesville, FL exposed female Ae. aegypti, An. albimanus and Cx. quinquefasciatus to LD25 levels of pyrethroid treatments (the dose necessary to kill only 25% of the mosquitoes). After exposure to the insecticides, the flight paths of mosquitoes towards attractants in a wind tunnel were changed. Mosquitoes treated with insecticides tended to fly a less direct route to the attractant and fewer of them responded to the attractant after 24 hours. This suggests that pyrethroids may have a greater impact on disease transmission than their immediate killing impact.
Studies to determine potential nectar producing plants for mosquitoes. ARS researchers at Gainesville, FL, conducted a year-long study on the phenology of flowering plants (including shrubs and trees) in North Central Florida. The duration of flowering varied, but for most plant species was 2-4 weeks. The volatile chemical profile, which is used by mosquitoes to locate potential nectar sources, was determined for 30 plant species. This information will be used to develop synthetic nectar attractant lures for use with traps/targets in integrated mosquito management programs. Most mosquitoes seek a nectar meal before they blood feed, thus traps baited with such a synthetic lure may reduce the number of mosquitoes seeking a blood meal.
Mosquito behavior in the presence of attractants, repellents and insecticides. Repellents and insecticides are the principal methods for preventing adult mosquitoes from feeding on humans however the impact of DEET (N,N-diethyl-3-methylbenzamide) and pyrethroids on mosquito behavior is poorly understood. Furthermore, the mode of action of DEET is not clearly defined but it is thought to block the ability of mosquitoes to detect specific human odors. ARS researchers in Gainesville, FL filmed the flight behavior of host-seeking female Ae. aegypti and Anopheles in the presence of pyrethroid and DEET-treated uniforms. Researchers found mosquitoes always detected the presence of the blood meals as indicated by their flight towards the blood meal, therefore, DEET did not mask the odors. However, both the DEET and pyrethroid treatment reduced the number of mosquitoes taking blood meals. Mosquitoes attempting to feed through the DEET attempted to feed but were later repelled and after 10 minutes the majority had stopped trying to feed. In the pyrethroid treatment, mosquitoes tried to feed throughout the entire 20 minute trial and this continued contact with the treated substrates often resulted in 10% mortality of the mosquitoes. Neither repellent or insecticide created a spatial barrier or prevented mosquitoes from landing and attempting to feed through the treated material.
Determine factors that result in positive resting site selection responses by adult Culex. Backpack aspirator (suction) samples of resting adult mosquito populations in a Florida swamp (Sumter County) indicate that tree stumps and exposed tree root systems are preferred refugia. Three dozen of these natural resting site structures have been identified for study by ARS scientists in Gainesville, FL, in twelve field plots and Global Positioning System (GPS) coordinates for each of the sites recorded, with additional locations in each plot designated for placement of artificial resting shelters. Initial observations of mosquito resting activity indicate that selection/avoidance of resting sites by Culex species is related to light intensity and resting surface temperature.
Semi-field evaluations of visual lures to attract the Asian Tiger Mosquito. Cylindrical traps covered with fabric of a range of colors (white, black, red, dark blue, and dark yellow) or contrasting patterns were evaluated against laboratory-reared Asian Tiger Mosquitoes under semi-field conditions. Cylindrical traps with contrasting patterns of dark/light (especially horizontal alternating bands of black and white) were the most attractive. The impact of this study by ARS scientists in Gainesville, FL will be the development of more effective traps.
Development of larval mosquito attraction assays. Surveillance of mosquito larvae is a critical step guiding targeted control for mosquitoes that are pests or vectors of livestock and human diseases such as viral encephalitis and dengue. The current method of dipping provides an inaccurate estimate of numbers and species of larvae present. With the target of development of an attractant-based surveillance method, ARS researchers at Gainesville, FL devised a dual-choice larval attraction assay method effective for screening potential attractants. Larvae of Ae. aegypti were highly attracted to food materials (i.e., fish food, liver powder, yeast) and demonstrated dose-dependent responses to chemicals associated with microbial degradation in water. These results provide the basis for the discovery of effective larval attractants that would provide a novel monitoring tool for mosquito larvae.
Characterize environmental predictors of mosquito distribution in time and space. Three 1 hectare study plots have been identified in a Florida swamp (Sumter County). GPS coordinates for the location of adult mosquito traps within each study plot are being gathered by ARS scientists in Gainesville, FL, and image analysis and ground-based study methods are being used to identify the physiographic and vegetation characteristics of each plot for incorporation in a geographic information system (GIS).
Built upon 2006-2009 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. ARS scientists in Gainesville, FL were part of a team predicted the ongoing RVF outbreak in South Africa, leading to early detection and World Health Organization warnings for international travelers going to South Africa for the 2010 Soccer World Cup. They also issued early warnings for Kenya leading to animal vaccination and mosquito control which may have may have prevented an outbreak. Additionally, these predictions also protected the U.S. and other non-endemic countries from potential introductions of this exotic disease. MFRU staff maintained the organization of 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 sets a trajectory that will significantly strengthen and protect the U.S. against the possible arrival of RVFV as well as other mosquito-borne viruses currently or potentially impacting the U.S. economy and public and veterinary health. MFRU staff participated in international RVF meetings in the U.S. and Nairobi, Kenya, and published a landmark article in the Proceedings of the National Academy of Sciences on the successful prediction of the 2006-2007 RVF outbreak in Africa.
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Reinert, J.T. 2010. Comparative anatomy of the female genitalia of generic-level taxa in tribe Aedini (Diptera: Culicidae). Part XXXIII. Genus Lewnielsenius Reinert, Harbach and Kitching. Contributions to the American Entomological Institute. 36(2):21-30.
Reinert, J.F. 2010. Comparative anatomy of the gemale genitalia of generic-level taxa in tribe Aedini (Diptera: Culicidae). Part XXXIV. Genuus Catageiomyia Theobold. Contributions of the American Entomological Institute. 36(2):31-42.
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Reinert, J.F. 2010. Comparative anatomy of the female genitalia of generic-level taxa in tribe Aedini (Diptera: Culicidae). Part XXXI. Genus Sallumia Reinert, Harbach and Kitching. Contributions of the American Entomological Institute. 36(2):1-20.