SAMPLING BIAS IN DETERMINING THE PAROUS RATE OF COLLECTIONS OF CULICOIDES BREVITARSIS KIEFFER AND C-WADAI KITAOKA (DIPTERA, CERATOPOGONIDAE)

Culicoides brevitarsis and C. wadai were collected using two updraught light traps which were run simultaneously for 107 nights. One trap, t ermed + 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 colle ctions of both species were also made. The parous rates of C. wadai fr om - cattle and + cattle collections and from + cattle and sweep-net c ollections were similar suggesting that light traps provide collection s that are as representative of the biting population as that provided by sweep-net collections and that the proximity of cattle to the ligh t trap has little effect on the parous rate of collections. This means that light traps are suitable for use in survival rate studies of thi s species and are not affected by the proximity of cattle. For C. brev itarsis, however, - cattle collections had higher parous rates than cattle collections which in turn had higher parous rates than sweep-ne t collections of this species. This suggests that light traps are pron e to bias and that estimates of survival of C. brevitarsis based on th e parous rate of light-trap collections are likely to be more accurate when traps are placed in close proximity to cattle. The mean parous r ate of C. brevitarsis from light-trap collections in the presence of c attle (0.461) was significantly higher (P < 0.01) than that of C. wada i (0.313), suggesting that the former species has a higher rate of sur vival and is therefore likely to be a more important vector than the l atter.