Overwintering of Culicoides spp. (Diptera: Ceratopogonidae) in the Hunter Valley, New South Wales

In a study of the overwintering ability of Culicoides spp, at the southern limits of the distribution of Culicoides brevitarsis Kieffer, it was found that C. brevitarsis numbers declined linearly with temperature during winter but were independent of rainfall. Regression equations were used to calculate lower thresholds for C. brevitarsis activity/presence. These thresholds were similar for three different collection methods. Results obtained from light trap data for four other Culicoides spp showed that their relationship with temperature allowed their recovery after winter. Under suitable conditions, oviposition by C. brevitarsis continued into winter and immature stages survived for 1 to 2 months (mainly as pupae/pre-pupae) in cattle dung, its breeding habitat. Survival of C. brevitarsis was affected by the time spent at temperatures below the estimated thresholds. Reinfestations from coastal regions further north could be responsible for the reappearance of C. brevitarsis in years when they fail to survive in the central coastal region of NSW. Conversely, the other Culicoides spp. recorded appeared capable of maintaining viable populations.