Impact of mechanical disturbance on the emergence of Culicoides from cowpats

Abstract

The outbreaks of Bluetongue virus and Schmallenberg virus between 2006 and 2012 highlighted the need for control methods for north-western Palaearctic biting midge species. There is especially a demand for alternative control methods without application of insecticides. Therefore, the objective of this paper was to evaluate the impact of mechanical disturbance as a control method for Culicoides biting midges in cowpats. We used a trash rake to destroy the compact structure of cowpats and spread the dung over the ground. We expected the disturbance to cause a faster alteration of physical characteristics and drying of the dung, resulting in lower emergence from disturbed cowpats. Emerging biting midges were collected with emergence traps. The number of emerged Culicoides was compared between treated and control cowpats. A total of 12,979 biting midges emerged, all belonging to the Obsoletus group. The majority of the 6,758 male individuals were identified as Culicoides chiopterus (Meigen, 1830) (91.4%), followed by Culicoides dewulfi (Goetghebuer, 1936) (6.5%), and a small number of Culicoides scoticus (Downes & Kettle, 1952) (1.2%). Our results showed no significant differences between the emergence of Culicoides (males and females) from disturbed and control cowpats. The lack of differences is discussed in light of the time period chosen for the experiment and the climatic conditions (especially low temperatures) during the study period. The climatic conditions during the study did not favour desiccation effects and therefore did not cause a severe alteration of the dung and the biotic parameters. In conclusion, immature Culicoides showed a high tolerance against mechanical disturbance.