E. T. Schmidtmann

Sympatry in the Culicoides variipennis complex (Diptera: Ceratopogonidae): a taxonomic reassessment.

Abstract We report sympatry among larval populations of the Culicoides variipennis complex in widespread and diverse aquatic habitats throughout the United States. Six sites in California, Nevada, New Mexico, and Texas were co-inhabited by C. v. occidentalis and C. v. sonorensis, whereas 8 sites in Florida, Georgia, Louisiana, Maryland, and Texas were co-occupied by C. v. sonorensis and C. v. variipennis. No intermediate forms were identified either electrophoretically or morphologically in adults reared from field-collected larvae and pupae. The absence of intergrades in zones of sympatry represents sufficient evidence to confirm species status for Culicoides variipennis (Coquillett) and Culicoides occidentalis Wirth & Jones, and to elevate Culicoides sonorensis to species rank (NEW STATUS). Culicoides v. albertensis Wirth & Jones is a synonym of C. sonorensis (NEW SYNONYMY); C. v. australis Wirth & Jones also is confirmed as a synonym of C. sonorensis. We also demonstrated a correlation between population taxonomic status as determined by electrophoresis and adult morphology.

Mosquito Larval Habitat Mapping Using Remote Sensing and GIS: Implications of Coalbed Methane Development and West Nile Virus

Abstract Potential larval habitats of the mosquito Culex tarsalis (Coquillett), implicated as a primary vector of West Nile virus in Wyoming, were identified using integrated remote sensing and geographic information system (GIS) analyses. The study area is in the Powder River Basin of north central Wyoming, an area that has been undergoing a significant increase in coalbed methane gas extractions since the late 1990s. Large volumes of water are discharged, impounded, and released during the extraction of methane gas, creating aquatic habitats that have the potential to support immature mosquito development. Landsat TM and ETM+ data were initially classified into spectrally distinct water and vegetation classes, which were in turn used to identify suitable larval habitat sites. This initial habitat classification was refined using knowledge-based GIS techniques requiring spatial data layers for topography, streams, and soils to reduce the potential for overestimation of habitat. Accuracy assessment was carried out using field data and high-resolution aerial photography commensurate with one of the Landsat images. The classifier can identify likely habitat for ponds larger than 0.8 ha (2 acres) with generally satisfactory results (72.1%) with a lower detection limit of ≈0.4 ha (1 acre). Results show a 75% increase in potential larval habitats from 1999 to 2004 in the study area, primarily because of the large increase in small coalbed methane water discharge ponds. These results may facilitate mosquito abatement programs in the Powder River Basin with the potential for application throughout the state and region.

Soil chemistries define aquatic habitats with immature populations of the Culicoides variipennis complex (Diptera: Ceratopogonidae).

Abstract Aquatic habitats with immature populations of the Culicoides variipennis (Coquillett) complex were sampled across the United States and tested for soil chemistry parameters. Indicators of organic loading, phosphate, percentage of organic matter, and nitrate were high for C. variipennis and C. sonorensis, reflecting the common occurrence of larvae in sediments contaminated with livestock waste; these factors were low in western playa lake habitats with immature C. occidentalis. Levels of salt-forming ions and indicators of salinity, notably sodium, chloride, magnesium, sulfate, boron, and conductivity, were elevated in substrates supporting all 3 species, with values that declined from very high to high across the arid west to moderate east of the Mississippi river, and differed significantly among species. Concentrations of boron differed most strongly among habitats of the respective species, ranging from exceptionally high values in playa lake substrates with C. occidentalis, to high and moderate levels in western and southeastern sites with C. sonorensis, to moderate levels for substrates in the east with C. variipennis. The presence of C. sonorensis in dairy wastewater lagoons and saline springs in geographic regions that are otherwise inhabited by C. variipennis may reflect salinity factors that regulate the distribution of the C. variipennis complex.

Testing the Relationship Between Dissolved Salts in Aquatic Habitats and Immature Populations of the Culicoides variipennis Complex (Diptera: Ceratopogonidae)

Abstract Biting midges of the Nearctic Culicoides variipennis complex, C. sonorensis Wirth and Jones, C. variipennis (Coquillette), and C. occidentalis Wirth and Jones, are widespread and locally abundant throughout the United States. An understanding of environmental factors associated with the distributions of respective species is of value because risk for bluetongue disease in livestock is defined by the distribution of C. sonorensis, the primary vector of bluetongue viruses in the United States. This study tested the relationship between dissolved salts and immature populations of the C. variipennis complex by examining widespread and diverse aquatic habitats with larval populations and using discriminant analysis to classify larval habitats by species on the basis of soil chemistry. Aquatic habitats with immature C. sonorensis in British Columbia, Illinois, New Mexico, and Washington were moderate-high in levels of dissolved salts, as is typical for habitats with this species. In contrast, a nearby site with the sister species C. variipennis in British Columbia, as well as aquatic habitats in Illinois, were low in dissolved salts, similar to habitats with this species in the eastern United States. A saline stream in central Washington with C. occidentalis was extremely high in dissolved salts, like the playa lakes where this species occurs in the far western United States, whereas a stock pond near the saline stream was lower in dissolved salts and occupied by C. sonorensis. These data confirm that conspecific populations of the C. variipennis complex occur in habitats that have similar levels of dissolved salts, which differ between species, regardless of geographic location. Reverse stepwise discriminant analysis using new and archived soil chemistry data showed that electrical conductivity and chloride discriminated best between habitats with C. variipennis or C. sonorensis and that the combination of electrical conductivity and calcium had the most power of discrimination between habitats with C. sonorensis or C. occidentalis. Collectively, these findings represent convincing evidence that levels of dissolved salts influence the suitability of aquatic habitats for immature populations the C. variipennis complex and hence in part determine respective species’ distributions.