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item Schmidtmann, Edward

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2006
Publication Date: 10/1/2006
Citation: Schmidtmann, E.T. 2006. Testing the relationship between dissolved salts in aquatic habitats and immature populations of the culicoides variipennis complex (diptera:ceratopogonidae). Environmental Entomology 35(5):1154-1160.

Interpretive Summary: Biting midges of the Culicoides variipennis species complex occur across the United States, but the three species are found in specific geographic regions. The primary vector of bluetongue viruses, C. sonorensis is primarily a western species, but it also occurs in the Gulf Coast states and up the Atlantic seaboard to Maryland. This study was conducted to examine the possibility that differences exist in the chemical make up of sediments (mud) in aquatic habitats where the larval stages of the three species are found. Such differences may determine why one species occurs in one region of the U.S., whereas other species occur in other areas. In conducting this study, we took samples of sediments from habitats with larvae of the three species from across the U.S. The samples were sent to the University of Wyoming where they were tested in the Soils Laboratory for 13 chemical factors. The results show that levels of nitrate, phosphate and organic matter were high for the two most common species, reflecting the fact that they are commonly found in aquatic sites contaminated with livestock manure. Levels of salts, such as sodium, chloride, magnesium, boron and electrical conductivity (a measure of salts in general) were high for all three species, and ranged from very high to high across the arid west, to modertate levels east of the Mississippi river where greater rainfall dilutes levels of salts in surface soils. Importantly, levels of ceratin salts differed between the three species, and thus may be important in determining the distribution of the species. This understanding helps to explain why the species that transmits bluetongue virus is uncommon east of the Mississippi river where rainfall dilutes levels of salts in soils. It also may help to more accurately map the distribution of the species that do not transmit bluetongue virus, and this can benefit the export of U.S. livestock to other countries that do not have the disease.

Technical Abstract: Sediments from geographically diverse aquatic habitats with immature populations of the Culicoides variipennis complex (Diptera: Ceratopogonidae) were examined as a test of the relationship between dissolved salts and presence of respective species. Analysis of samples from British Columbia, New Mexico, Illinois, and Washington confirmed that populations of C. sonorensis Wirth and Jones occur in sediments with moderate to high levels of dissolved salts. Sediments from Illinois and central British Columbia with C. variipennis Wirth and Jones had low dissolved salts, as is typical for this species. Sediments from a saline stream in central Washington with C. occidentalis Wirth and Jones were extremely high in dissolved salts, like the concentrated salts of playa lakes where this species occurs across the far West. In contrast, dissolved salts in a nearby stock pond with C. sonorensis were much lower, like other manure-contaminated aquatic habitats that support this species. These data show that conspecific populations in geographically disparate habitats have similar soil chemistries, whereas sister species in proximal habitats have differing soil chemistries. Reverse stepwise discriminant analysis showed that levels of electrical conductivity and chloride discriminated best between habitats with C. variipennis and C. sonorensis; combining electrical conductivity with calcium had the most power of discrimination for habitats with C. sonorensis and C. occidentalis. These findings illustrate that the geographic distribution and suitability of aquatic habitats with immature populations the C. variipennis complex are strongly influenced by dissolved salts.