Evaluation of vegetation management strategies for controlling mosquitoes in a southern California constructed wetland

The abundance of mosquito larvae and adult production were measured in 3 vegetation treatments and 2 species of emergent macrophytes in replicated wetland mesocosms (12 x 80 m). During the 8-wk study, no significant differences were found in abundances of larvae and emerging adult mosquitoes among the vegetation treatments: 100% of the surface area in emergent vegetation, 50% of the surface area in emergent vegetation in 5-m-wide rows, and 50% of the surface area in emergent vegetation in 10-m-wide rows. Mosquito larvae (predominantly Culex tarsalis and Anopheles hermsi) were significantly more abundant in inundated bulrush (Schoenoplectus californicus) than in inundated cattail (Typha sp.). Adult emergence from vegetated zones containing bulrush also was significantly greater than from cattail. The failure of reduced emergent vegetation coverage to provide a significant reduction in mosquito production from the vegetated zones of the wetlands might have been caused by favorable conditions for mosquito oviposition and larval development after vegetation management and by the ineffectiveness of mosquito predators in emergent vegetation. A 50% reduction of vegetation did not significantly reduce the water quality of the wetland effluent; however, narrower rows (<5 m wide) of vegetation may be required to reduce mosquito production from vegetated regions of the treatment wetlands. Even though the abundance of mosquito larvae in open water is typically less than in emergent vegetation, creation of open-water zones in shallow treatment wetlands (<1 m depth) by drying the wetland followed by removal of emergent vegetation with heavy equipment is unlikely to provide a significant long-term reduction of mosquito production.     

Mermithid nematode parasites of Coquillettidia perturbans in Massachusetts.

We surveyed 792 larval and 12,400 adult Coquillettidia perturbans for mermithid nematodes in 1990. Collections were made from cattail marshes in the greater Boston area. No mermithids were found in the adult mosquitoes, nor in larvae collected in mid-season, but 3 were found in larvae collected during September and October. This is only the second recorded occurrence of mermithids in Cq. perturbans.     

Distribution of Culex tarsalis larvae in a freshwater marsh in Orange County, California

The distribution and abundance of mosquito larvae in a freshwater marsh were determined during a low water period in the late summer. Culex tarsalis larval abundance was significantly associated with the percent cover by Typha spp. root masses and Typha spp. stem density in 1-m2 quadrants. Larval mosquito abundance was not significantly related to bulrush (Scirpus californicus) stem density, position in the marsh (transect compass direction), position in the inundated vegetation on each transect or several physicochemical factors. As water levels decline seasonally, mosquito developmental sites in San Joaquin Marsh change from mats of decaying vegetation to cattail root masses.     

The runnelling method of habitat modification: an environment-focused tool for salt marsh mosquito management

Traditional methods of managing salt marsh mosquitoes focus primarily on maximizing the reduction of mosquito populations, with minimizing environmental impact as a secondary consideration. An environment-oriented approach to salt marsh management for mosquito control, runnelling, is described and compared with other forms of habitat modification such as ditching and Open Marsh Water Management (OMWM). Runnelling alters the salt marsh as little as possible while causing significant reductions in mosquito numbers. The effect of runnelling on the environment was monitored via the following variables: water table level, substrate characteristics (moisture, salinity and pH), vegetation (height and density of each Sporobolus virginicus) and the numbers of mosquito larvae. Runnelling had a statistically significant effect on only two of the seven variables. These were the height of Sporobolus, which increased near runnels, and the number of mosquito larvae, which decreased. The main difference between ditching, OMWM and runnelling lies in the magnitude of the habitat modification. Ditching involves the greatest alteration to the marsh, and runnelling the least. Consequently, runnelling has a smaller effect on the estuarine environment as a whole than does either ditching or OMWM.     

Mosquitoes associated with US Department of Agriculture managed wetlands on Maryland's DelMarVa Peninsula

Mosquito faunal studies were carried out 2004-2005 in Maryland's Eastern Shore wetlands managed by the US Department of Agriculture. The wetlands included flooded fields, inundated woodlands, and tidal salt marshes. Sampling methods included larval collections, adult landing counts, and CDC light and oviposition traps. A total of 1,186 larvae and 1,363 adults identified represented 14 species. Temporary pools were found to have the highest potential for rapid mosquito colonization with Psorophora columbiae the predominant species. Aedes vexans, Culex territans/pipiens, Ps. ciliata/howardii, and Anopheles crucians were collected primarily from pond and flooded woodlands. Ochlerotatus sollicitans larvae were sampled from tidal pools. The predominant daytime landing count species was Oc. sollicitans with Ps. ciliata, Ae. vexans, and Cx. territans also identified. Light traps collected An. crucians, the principal crepuscular species from flooded wooded areas. Aedes atlanticus, An. quadrimaculatus, Coquillettidia perturbans, Cx. restuans, Oc. sollicitans, Ps. ciliata, Ps. columbiae, and Uranotaenia sapphirina were also identified. Oviposition traps collected small numbers of An. crucians at the tidal marsh, 1 Ae. albopictus, and 1 each of Cx. territans/pipiens from the flooded woodlands. As a result of this study, it was recommended that abatement strategies be implemented during and after wetland construction to minimize the creation of temporary pool breeding sites.     

Comparisons of mosquito populations before and after construction of a wetland for water quality improvement in Pitt County, North Carolina, and data-reliant vectorborne disease management

Wetlands serve an important purpose in flood control and water quality, but constructed-wetland sites also provide habitats for mosquito breeding. Communities near constructed-wetland sites often raise a "mosquito" objection when constructed wetlands are proposed. Wildlife and wetland advocates can confuse the public by making unsubstantiated claims about natural predators eliminating or controlling mosquito problems in a constructed wetland. Management of constructed-wetland mosquito habitat, with adequate mosquito surveillance and data analysis, can help lead to a successful project and satisfied citizens. The cooperative project described in this paper, was conducted in the town of Simpson, North Carolina, and was designed to determine the mosquito population impact of wetland construction at Mill Branch Stream, a small tributary of the Tar River in Eastern North Carolina. In the authors' analysis of three years of mosquito surveillance data, month (time of year standing in for temperature and day length) was a significant factor in regression analysis for mosquito numbers, but rainfall was not. Numbers of mosquitoes were not found to be significantly higher after construction than before construction.     

Impact of oil-sands based wetlands on the growth of mallard (Anas platyrhynchos) ducklings

Identifying the potential effects of industrially formed wetlands on waterfowl populations is important for assessing the suitability of such wetlands in industrial reclamation strategies. Mallard ducklings were held in situ on two industrially formed wetlands and one reference wetland in northern Alberta, Canada. Duckling mass and skeletal size were measured at regular intervals over 33 d, and blood was collected to investigate the analysis of plasma metabolites (triglyceride and glycerol) as an indicator of physiological condition. In repeated-measures analysis of variance (ANOVA), multivariate ANOVA, and subsequent multiple-comparisons tests, body mass and skeletal size were significantly lower in ducklings maintained on the industrial wetland after 2, 5, 9, and 13 d of exposure. In this situation, plasma metabolite analysis did not provide additional information on mass-independent condition. We conclude that if the observed differences in growth and size translate into a decreased survival of juvenile waterfowl inhabiting these wetlands, then populations of these birds in the area could be negatively affected. We emphasize the importance of field-based ecological research in toxicological studies of wildlife.     

Application of geographic information technology in determining risk of eastern equine encephalomyelitis virus transmission

Geographic information system (GIS) technology and remote sensing were used to identify landscape features determining risk of eastern equine encephalomyelitis virus (EEE) transmission as defined by the abundance of Culiseta melanura (the enzootic vector) and 6 putative epidemic-epizootic vectors in Massachusetts. Landsat Thematic Mapper data combined with aerial videography data were used to generate a map of landscape elements at epidemic-epizootic foci in southeastern Massachusetts. Geographic information system technology was used to determine the proportion of landscape elements surrounding 15 human and horse case sites where abundance data were collected for Culiseta melanura, Aedes canadensis, Aedes vexans, Culex salinarius, Coquillettidia perturbans, Anopheles quadrimaculatus, and Anopheles punctipennis. The relationships between vector abundance and landscape proportions were analyzed using stepwise linear regression. Stepwise regression indicated wetlands as the most important major class element, which accounted for up to 72.5% of the observed variation in the host-seeking populations of Ae. canadensis, Ae. vexans, and Cs. melanura. Moreover, stepwise linear regression demonstrated deciduous wetlands to be the specific wetland category contributing to the major class models. This approach of utilizing GIS technology and remote sensing in combination with street mapping can be employed to identify deciduous wetlands in neighborhoods at risk for EEE transmission and to plan more efficient schedules of pesticide applications targeting adults.     

Geostatistical evaluation of integrated marsh management impact on mosquito vectors using before-after-control-impact (BACI) design

Background  

In many parts of the world, salt marshes play a key ecological role as the interface between the marine and the terrestrial environments. Salt marshes are also exceedingly important for public health as larval habitat for mosquitoes that are vectors of disease and significant biting pests. Although grid ditching and pesticides have been effective in salt marsh mosquito control, marsh degradation and other environmental considerations compel a different approach. Targeted habitat modification and biological control methods known as Open Marsh Water Management (OMWM) had been proposed as a viable alternative to marsh-wide physical alterations and chemical control. However, traditional larval sampling techniques may not adequately assess the impacts of marsh management on mosquito larvae. To assess the effectiveness of integrated OMWM and marsh restoration techniques for mosquito control, we analyzed the results of a 5-year OMWM/marsh restoration project to determine changes in mosquito larval production using GIS and geostatistical methods.     

Distribution and abundance of larval Coquillettidia perturbans in a Florida freshwater marsh

All instars of larval Coquillettidia perturbans were found in the same habitats, but early instar larvae were more aggregated than later instars. Larvae were most numerous in areas dominated by arrow-arum (Peltandra virginica) and maidencane (Panicum hemitomon), less so in areas dominated by sedges (Carex spp.) and miscellaneous mixed vegetation, and least abundant in pickerelweed (Pontederia cordata) areas. Larvae were uncommon in open water or in areas dominated by small floating plants such as water fern (Salvinia rotundifolia), duckweekd (Lemna minor) and mosquito fern (Azolla caroliniana). Larval concentrations were greatest in water 35-70 cm deep. There was also a tendency for them to concentrate in areas beyond 25 m from shore. Larvae were log-normally distributed in favorable sites and became progressively more aggregated as sites became less favorable.     

Acid sulfate soils in intertidal mosquito breeding habitats and implications for habitat modification

Public concern about the use of chemicals for mosquito control in coastal Australia has lead to the development of physical habitat modification methods that aim to reduce mosquito populations to acceptable levels. Habitat modification methods include runnels (depth < 0.30 m) and ditches (depth > 0.50 m). During excavation for habitat modification, a risk of exposure of acid sulfate soils may exist. Acid sulfate soils are soils that contain iron sulfides, in particular pyrite (FeS2), and produce sulfuric acid when exposed to air. These soils occur predominantly in coastal lowland areas that are also prime mosquito breeding habitats. The paper discusses the problem and illustrates the application of survey methods that facilitate wise decision making and management of intertidal wetlands.     

Stormwater ponds, constructed wetlands, and other best management practices as potential breeding sites for West Nile virus vectors in Delaware during 2004

We performed longitudinal surveys of mosquito larval abundance (mean mosquito larvae per dip) in 87 stormwater ponds and constructed wetland in Delaware from June to September 2004. We analyzed selected water quality factors, water depth, types of vegetation, degree of shade, and level of insect predation in relation to mosquito abundance. The 2004 season was atypical, with most ponds remaining wet for the entire summer. In terms of West Nile virus (WNV) vectors, wetlands predominantly produce Aedes vexans, culex pipiens pipiens, and Culex restuans. Retention ponds generally produced the same species as wetlands, except that Cx. p. pipiens was more abundant than Cx. restuans in retention ponds. Aedes vexans and Culex salinarius were the most abundant species to Conservation Restoration Enhancement Program ponds. Sand filters uniquely produced high numbers of Cx. restuans, Cx. p. pipiens, and Aedes japonicus japonicus, a newly invasive vector species. Site that alternately dried and flooded, mostly detention ponds, forebays of retention ponds, and some wetlands often produced Ae. vexans, an occasional WNV bridge vector species. Overall, seasonal distribution of vectors was bimodal, with peaks occurring during early and late summer. Ponds with shallow sides and heavy shade generally produced an abundance of mosquitoes, unless insect predators were abundant. Bright, sunny ponds with steep sides and little vegetation generally produced the fewest mosquitoes. The associations among mosquito species and selected vegetation types are discussed.     

An evaluation of the mosquitofish, Gambusia affinis, and the inland silverside, Menidia beryllina, as mosquito control agents in California wild rice fields

The mosquitofish, Gambusia affinis, and the inland silverside, Menidia beryllina, were evaluated in experimental, one-tenth hectare wild rice plots in Lake County, California, for their impact on densities of Culex tarsalis, Anopheles freeborni and Anopheles franciscanus. Gambusia affinis were tested at 0.6 and 1.7 kg/ha and the silversides at ca. 0.9 kg/ha. The silversides did not survive well in the rice field system and none of the silverside guts examined contained mosquito larvae. The mosquitofish increased steadily throughout the season and mosquito larvae were found in 9% of the fish dissected. Analysis of variance did not reveal significant differences among the mosquito populations in the 3 fish treatments and controls on any sampling date. More than 40 species of aquatic insects were collected and population densities of selected aquatic insects were similar among the 4 treatments.     

Immature mosquitoes of Serra do Mar park, Sao Paulo State, Brazil

With the objective of providing knowledge about the natural habitat of mosquito larvae, we conducted a study on the culicid fauna and identified larval habitat types at 3 different locations in the Serra do Mar State Park, Brazil, over the 12 months of 1991. We collected 1,425 larvae belonging to 23 species, of which the most frequent were Culex iridescens, Culex spp., Limatus durhami, and Trichoprosopon pallidiventer. The mosquito larval habitats presenting the greatest densities of specimens were bamboo, bromeliads, rubber boots, and streams. We observed that the culicids used a variety of containers as larval habitats and bred under a diversity of ecological conditions. Most of the habitats were natural, formed by bamboo, bromeliads, streams, and depressions in the ground and in rocks, along with artificial habitats consisting of rubber boots and abandoned metal cans. Seven species occurred preferentially in the internodes of closed bamboo stems, 6 in internodes of open stems, and 4 in bromeliads.     

Distribution of resting female Aedes vexans (Meigen) in wooded and nonwooded areas of metropolitan Minneapolis-St. Paul, Minnesota.

Daytime resting mosquito densities in 4 habitat types (wooded, residential yard, garden, and crop) were examined to determine if areas other than wooded ones may be serving as prime mosquito resting habitat. Adult Aedes vexans were collected in the Minneapolis-St. Paul metropolitan area with large battery-powered aspirators to determine mosquito densities at randomly chosen sites within the metropolitan area that supported all 4 habitats. Measurements were taken to estimate the total area of each habitat type within the sample areas. The highest densities of mosquitoes were found in wooded areas. Although agricultural crop areas had relatively low mosquito densities, they supported the 2nd largest number of mosquitoes because of the extremely large cropland area. Residential yards and gardens contained fewer mosquitoes compared with wooded areas. A greater percentage of bloodfed mosquitoes was collected within the wooded habitat.     

Design and Construction of Wetlands for Aqueous Transfers and Transformations of Selected Metals

Two pilot-scale wetland cells (6.1 × 30.5 m) were integratively designed and constructed to emphasize and enhance transfers and transformations of selected metals (Cu, Pb, and Zn) in an aqueous matrix. A series of preliminary experiments and analyses were conducted to select macrofeatures (hydroperiod, hydrosoil, and vegetation) of the constructed wetland system. These wetland cells were designed to operate in series or parallel with nominal hydraulic retention times of 24–48 hr, respectively. With water at a depth of 30 cm, both wetland cells had hydrosoil (45 cm) planted withScirpus californicus.After 250 days of wetland operation, average hydrosoil redox potentials in each wetland cell decreased from +90 mV to −165 mV, and average plant height increased from 0.3 to 2.7 m. Aqueous samples were collected over a 4.5-month period at the inflow and outflow sites of the wetland cells. Average inflow concentrations of total recoverable Cu, Pb, and Zn were 22.4, 10.5, and 565.9 μg/L, respectively. After a 46-hr HRT, average outflow concentrations of total recoverable Cu, Pb, and Zn were 15, 2.2, and 85.9 μg/L, resulting in removals of 33, 79, and 85%, respectively. Initial results suggest that these constructed wetlands can be designed to remove targeted metals in wastewater.     

Transfers and transformations of zinc in flow-through wetland microcosms.

Two microcosm-scale wetlands (570-liter containers) were integratively designed and constructed to investigate transfers and transformations of zinc associated with an aqueous matrix, and to provide future design parameters for pilot-scale constructed wetlands. The fundamental design of these wetland microcosms was based on biogeochemical principles regulating fate and transformations of zinc (pH, redox, etc.). Each wetland consisted of a 45-cm hydrosoil depth inundated with 25 cm of water, and planted with Scirpus californicus. Zinc ( approximately 2 mg/liter) as ZnCl2 was amended to each wetland for 62 days. Individual wetland hydraulic retention times (HRT) were approximately 24 h. Total recoverable zinc was measured daily in microcosm inflow and outflows, and zinc concentrations in hydrosoil and S. californicus tissue were measured pre- and post-treatment. Ceriodaphnia dubia and Pimephales promelas7-day aqueous toxicity tests were performed on wetland inflows and outflows, and Hyalella azteca whole sediment toxicity tests (10-day) were performed pre- and post-treatment. Approximately 75% of total recoverable zinc was transferred from the water column. Toxicity decreased from inflow to outflow based on 7-day C. dubia tests, and survival of H. azteca in hydrosoil was >80%. Data illustrate the ability of integratively designed wetlands to transfer and sequester zinc from the water column while concomitantly decreasing associated toxicity.     

A laboratory study of predation by damselfly nymphs, Enallagma civile, upon mosquito larvae, Culex tarsalis

The nymph of the damselfly, Enallagma civile, feeds on the larvae of the mosquito Culex tarsalis amongst a variety of other small aquatic invertebrates. Average daily consumption of 3rd instar Cx. tarsalis larvae by the last nymphal stage of E. civile was 6.06 larvae (range 4.64-8.67). Experiments in which density of prey (mosquito larvae) and predators (E. civile nymphs) were varied, showed that more prey was consumed as prey density increased. However, fewer prey were consumed at higher predator densities; mutual interferences among predators at higher predator densities was suspected.     

An inexpensive intervention for the control of larval Aedes aegypti assessed by an improved method of surveillance and analysis

A sampling method coupled with statistical calibration factors was developed to accurately assess the numbers of larvae and pupae of Aedes aegypti in large water-storage containers of variable capacities and water levels. Aedes aegypti productivity in different types of breeding sites found in an urban study area in central Colombia was assessed and compared. In this study, water-storage tanks and drums were found to comprise 79% of the containers positive for larval Ae. aegypti, which contributed to 93 and 92% of the total production of populations of 4th-stage larvae and pupae, respectively. These main breeding sites of Ae. aegypti were found at an indoor to outdoor ratio of 2.4:1 and no correlation was found between temporal fluctuation of populations of larval Ae. aegypti and monthly rainfall. Netted lids that used inexpensive local materials were designed to prevent oviposition by Ae. aegypti. During a 6-month trial period, 56% of inspected containers had netted lids correctly in place. Of these, 78% had no mosquito larvae. Because only 37% of uncovered containers were free of mosquito larvae, a significant difference was demonstrated when these inexpensive mechanical barriers were used (chi2 = 138.7; P < 0.001). These netted lids and the improved methods described to assess the productivity of larval and pupal Ae. aegypti in this study are now being used in combination with other strategies to assess and control these populations of dengue virus vectors in the main port city on the Atlantic Coast of Colombia.     

岷县地震灾区积水蚊幼虫杀灭效果观察

目的观察10%高效氯氰菊酯悬浮剂常量喷雾施药对灾区积水蚊幼虫的杀灭效果,为震后蚊虫防治提供依据。方法选择灾区永星村两处蚊幼虫密度较高的积水,分别用10%氯氰菊酯悬浮剂500倍稀释水溶液进行施药处理与对照观察评价杀灭蚊幼效果。结果施药后10 min杀幼率达到99.04%,60 min杀幼率达到100%,在施药后6 h(360 min)杀幼率仍为100%。结论 10%氯氰菊酯悬浮剂500倍稀释水溶液对积水蚊幼虫有非常显著的杀灭效果。