Abstract:
Culicoides midges (Diptera: Ceratopogonidae), the vectors of economically important
arboviruses such as bluetongue virus and African horse sickness virus, are of global importance.
In the absence of transovarial transmission, the parity rate of a Culicoides population provides
imperative information regarding the risk of virus dispersal. Abdominal pigmentation, which
develops after blood feeding and ovipositioning, is used as an indicator of parity in Culicoides.
During oral susceptibility trials over the last three decades, a persistent proportion of blood engorged
females did not develop pigment after incubation. The present study, combining a number of feeding
trials and different artificial feeding methods, reports on this phenomenon, as observed in various
South African and Italian Culicoides species and populations. The absence of pigmentation in artificial
blood-fed females was found in at least 23 Culicoides species, including important vectors such
as C. imicola, C. bolitinos, C. obsoletus, and C. scoticus. Viruses were repeatedly detected in these
unpigmented females after incubation. Blood meal size seems to play a role and this phenomenon
could be present in the field and requires consideration, especially regarding the detection of virus in
apparent “nulliparous” females and the identification of overwintering mechanisms and seasonally
free vector zones.
