Abstract
The Sacramento (northern Central) Valley of California (CA) has a hot Mediterranean climate and a diverse ecological landscape that is impacted extensively by human activities, which include the intensive farming of crops and livestock. Waste-water ponds, marshes, and irrigated fields associated with these agricultural activities provide abundant larval habitats for C. sonorensis midges, in addition to those sites that exist in the natural environment. Within this region, C. sonorensis is an important vector of bluetongue (BTV) and related viruses that adversely affect the international trade and movement of livestock, the economics of livestock production, and animal welfare. To characterize the seasonal dynamics of immature and adult C. sonorensis populations, abundance was monitored intensively on two dairy farms in the Sacramento Valley from August 2012– to July 2013. Adults were sampled every two weeks for 52 weeks by trapping (CDC style traps without light and baited with dry-ice) along N-S and E-W transects on each farm. One farm had large operational waste-water lagoons, whereas the lagoon on the other farm was drained and remained dry during the study. Spring emergence and seasonal abundance of adult C. sonorensis on both farms coincided with rising vernal temperature. Paradoxically, the abundance of midges on the farm without a functioning waste-water lagoon was increased as compared to abundance on the farm with a waste-water lagoon system, indicating that this infrastructure may not serve as the sole, or even the primary larval habitat. Adult midges disappeared from both farms from late November until May; however, low numbers of parous female midges were detected in traps set during daylight in the inter-seasonal winter period. This latter finding is especially critical as it provides a potential mechanism for the “overwintering” of BTV in temperate regions such as northern CA. Precise documentation of temporal changes in the annual abundance and dispersal of Culicoides midges is essential for the creation of models to predict BTV infection of livestock and to develop sound abatement strategies.
Highlights
Members of the genus Culicoides are small (1–3 mm) hematophagous flies in the family Ceratopogonidae
A total of 79,348 and 48,039 adult C. sonorensis was collected from Farms A and B during 26 weeks of trapping, respectively; not significant, increased numbers of adults per trap-night were collected from Farm A than Farm B despite the lack of a functioning waste-water lagoon at the former site
With the highly notable exception of 32 parous females that were collected in daytime traps that were set on Farm B during February, 2013, C. sonorensis were not collected in traps set from late November, 2012 until May, 2013
Summary
Members of the genus Culicoides are small (1–3 mm) hematophagous flies (midges) in the family Ceratopogonidae. They occur throughout the inhabited world, where they serve as biological vectors of several pathogenic animal viruses, including bluetongue virus (BTV), epizootic hemorrhagic disease virus, African horse sickness virus, and Akabane and Schmallenberg viruses [1,2,3,4,5,6,7,8]. BTV infection is distinctly seasonal in temperate regions such as California (CA), where the vast majority of infections occur during the late summer and fall months [20,21,22,23]. Dairy waste-water holding ponds (lagoons) are considered to be the primary developmental sites for C. sonorensis on intensive commercial dairy farms in California, because the immature stages develop in mud within the littoral zone of the ponds, which is heavily enriched with excrement [29,30,31,32]
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