Culicoides biting midge density in relation to the position and substrate temperature in a cattle dung heap

Dung heaps offer warm breeding sites, which might be suitable for a continuing development or even emergence at low air temperatures in winter. Therefore, this study collected substrate samples from the outer surface and core of a cattle dung heap at the beginning of the winter period. We aimed to analyze the density of immature Culicoides in relation to substrate position and temperature. We took samples from the outer layer and core of the dung heap at different heights. Floatation was used to extract Culicoides larvae from the dung heap samples. In order to rear larvae individually, we separated them in glass tubes. A total of 229 Culicoides larvae were extracted from the dung heap samples. Highest densities (99.1% of all larvae) were recorded for the outer layers of the dung heap but hardly any in the core (0.9% of all individuals). While the density of larvae was negatively correlated with increasing substrate temperatures, Culicoides larvae were found in a temperature range between 7.9 and 38.0 °C (mean 16.6 °C). Extracted larvae were reared to adults. All male individuals were identified as Culicoides obsoletus (Meigen), 1818 and all female individuals as C. obsoletus/Culicoides scoticus. It can be concluded that dung heaps offer temperature conditions, which allow the survival and probably also the development to adults for immature Culicoides also under harsh climate conditions in winter.