Host-seeking activity of adult Culicoides sonorensis (Diptera: Ceratopogonidae) during winter in southern California, USA, and assessment of bluetongue virus overwintering

Abstract

In southern California, USA, annual reoccurrence of bluetongue infection in cattle (Bos taurus Linnaeus (Artiodactyla: Bovidae)) suggests that bluetongue virus (BTV) persists year-round but escapes detection during cooler months, reappearing when the weather gets warmer. The persistence of the virus in the adult biting midge vector, Culicoides sonorensis Wirth and Jones (Diptera: Ceratopogonidae), has been suggested. However, it is unknown whether adult C. sonorensis are sufficiently active during the winter months to transmit BTV throughout this period. This study captured host-seeking C. sonorensis in the Chino dairy region of southern California throughout the BTV interseasonal period (winter through early spring) over 3 years to assess adult host-seeking activity and adult survival during this period. BTV prevalence in host-seeking midges was also determined. Host-seeking nulliparous and parous C. sonorensis were consistently captured throughout the winter months, which combined with wintertime adult midge survival of ≤27 d, suggests the BTV overwintering is likely due to ongoing low-level transmission to available cattle hosts. However, BTV was not detected in midges captured during January through April in this study, suggesting that BTV transmission during the winter months may be occurring at too low a level to detect even with the substantial trapping effort applied in this study.

Immigration and seasonal bottlenecks: high inbreeding despite high genetic diversity in an oscillating population of Culicoides sonorensis (Diptera: Ceratopogonidae)

“…It should be noted that the number of adults collected in our traps may not reflect the true population size as there may be no reduction in the larval densities. However, for at least C. sonorensis , there is evidence that immature abundance also decreases during the winter months (Mullens and Lip 1987, Mayo et al 2014), and further evidence from this population suggests continuous immature development and emergence (Zhang and Gerry 2023). Regardless, our results suggest that factors other than adult abundance are responsible for the elevated levels of F IS commonly associated with populations of Culicoides biting midges.…”