Effect of temperature regimes on the development, survival and emergence of Culicoides brevitarsis Kieffer (Diptera: Ceratopogonidae) in bovine dung

Culicoides brevitarsis is a biting midge and a vector of several viruses affecting livestock in Australia. An emergence chamber for collecting Culicoides spp. from dung was evaluated to determine its suitability for the study of C. brevitarsis developing in dung at different temperatures in the laboratory. It enabled experiments to be carried out in the natural breeding medium, relative humidity to be maintained at high levels and temperature through the dung to be stabilised at treatment temperatures relatively quickly. C. brevitarsis emerged within a temperature range of 17 degrees C to 36 degrees C with the greatest numbers between 25 degrees C and 36 degrees C. Males were dominant at low temperatures and females were dominant at high temperatures. Development times (to 50% emergence from deposition of the dung) and response times (to 50% emergence after starting to emerge) were least at the highest temperatures. Development times at the same temperature differed between experiments and this was associated with the temperature in the field before the dung was placed at a temperature treatment. Some survival occurred outside the 17 degrees C to 36 degrees C range, but emergence was dependent on the temperature eventually being changed to a more suitable level. The approximate lower threshold for emergence was about 17 degrees C. At this temperature, numbers emerging were low, development was delayed significantly and none survived for more than 50 d. High numbers of adults started to emerge within 24 h from dung held at 17 degrees C for up to 42 d from the deposition of the dung when the temperature was raised to 25 degrees C or 28 degrees C. The results support field temperature data and were used in predicting the areas that may be free of the vector.