Effects of temperature and photoperiod on the development of overwintering immature Culicoides chiopterus and C. dewulfi

•We studied overwintering immature dung breeding Culicoides.•We examined the effect of temperature/photoperiod on the development period.•High temperatures triggered the development to adults.•Photoperiod had no significant impact on the development period.•Temperature is an important factor affecting the spring emergence of Culicoides. In areas with harsh winters, several studies have recorded low numbers – or even zero – adult Culicoides during the winter period followed by a population peak in the subsequent spring. This experimental study determined whether temperature, photoperiod, or the combination thereof affect the development of overwintering immature dung breeding Culicoides, resulting in this peak. Temperature had a significant impact on the development period of Culicoides chiopterus (Meigen), 1830 and C. dewulfi Goetghebuer, 1936. In treatments with constant high temperature, emergence occurred shortly after the beginning of the experiment (mean=day 9). In contrast, no individuals emerged from the other two treatments, as long as the temperatures were below 10°C. In these treatments, the emergence of Culicoides started when the temperature exceeded 20°C for some days (mean=day 33). There was no significant difference between the two photoperiods (February or April day length; 9h:15h [light:dark] vs. 13h:11h). Our results highlight the importance of temperature on the spring emergence of C. chiopterus and C. dewulfi, but the response to the four temperature-photoperiod treatments did not differ between the two species.