Sampling bias in determining the parous rate of collections of Culicoides brevitarsis Kieffer and C. wadai Kitaoka (Diptera Ceratopogonidae)

Abstract

Culicoides brevitarsis and C. wadai were collected using two updraught light traps which were run simultaneously for 107 nights. One trap, termed + cattle, was set next to a pen containing 10 cattle. The other trap, termed - cattle, was set 40 m away from the pen. Sweep-net collections of both species were also made. The parous rates of C. wadai from - cattle and + cattle collections and from + cattle and sweep-net collections were similar suggesting that light traps provide collections that are as representative of the biting population as that provided by sweep-net collections and that the proximity of cattle to the light trap has little effect on the parous rate of collections. This means that light traps are suitable for use in survival rate studies of this species and are not affected by the proximity of cattle. For C. brevitarsis, however, - cattle collections had higher parous rates than + cattle collections which in turn had higher parous rates than sweep-net collections of this species. This suggests that light traps are prone to bias and that estimates of survival of C. brevitarsis based on the parous rate of light-trap collections are likely to be more accurate when traps are placed in close proximity to cattle. The mean parous rate of C. brevitarsis from light-trap collections in the presence of cattle (0.461) was significantly higher (P < 0.01) than that of C. wadai (0.313), suggesting that the former species has a higher rate of survival and is therefore likely to be a more important vector than the latter.