Positions of Juvenile Stages of Culicoides brevitarsis Kieffer (Diptera: Ceratopogonidae) and of Four Other Flies in Bovine Dung

A study was made of the positions of juvenile stages of Culicoides brevitarsis and of four other species of flies (Diptera) breeding in bovine dung. The objective was to provide information on sampling cores of dung for laboratory experiments and to study fly behaviour associated with the breeding habitat. Oviposition and field exposure of dung were restricted to 2 d and this enabled relatively discrete populations of flies to be investigated. All species were reasonably abundant after 2 d of oviposition. Distributions were contrasted by dividing the dung into vertical and horizontal segments. C. brevitarsis, A ustralosepsis niveipennis and Leptocera mirabilis oviposited mainly in the top of the dung, while Sepsis nitens and Psychoda sp. oviposited mainly in the lower half. After hatching, the proportions of flies varied between positions and over time. Except for C. brevitarsis, the adult flies were reared from the half of the pat associated with oviposition. C. brevitarsis and A. niveipennis rearings were evenly distributed in centre and outer positions 4 d after dung deposition and C. brevitarsis showed clear changes in vertical position over time. Moisture content in the dung decreased by 16.1% after 10 d, mainly in the upper half of the pat. Greater numbers of C. brevitarsis were associated with areas of higher moisture. The fly species varied in their times of emergence with C. brevitarsis emerging later in the lower half positions than in the upper half positions 10 d after deposition of the dung. A procedure for sampling cores of dung is proposed.