Abstract
Ten species of horseflies, totally 2,000 individuals, were collected at 7 station in Toyama, Iwate or Aomori Prefecture, either by dry-ice trap or by sweeping. Their nectar-sucking behaviors were discussed after microscopic as well as chemical examinations on nectars ingested. 1. The overall nectar sucking rate in total individuals was 82%, among which, part of the large-sized horseflies, such as Tabanus chrysurus and T. katoi showing rather lower rate. The distribution of nectar-sucking degree was, fully-sucked 10%, and medium and few 36% each. 2. The largest quantity of nectars sucked was 41μl in T. chrysurus, 35μl in T. katoi, 20μl in T. rufidens and T. trigeminus, 14μl T. humilis and T. sapporoensis, and 13μl in T. iyoensis. 3. The sugar concentration of nectars sucked ranged from 16.6% to 77.5% and there seemed to exist a tendency that the smaller the size of the species, the higher the sugar concentration. 4. The distribution of nectars after ingestion was, in general, limited only in the diverticulum, while, in 24% of T. iyoensis, in 10% of T. sapporoensis and in 6% of T. rufidens, nectars were found also in the midgut. 5. Paper chromatographic analysis of nectars indicated that 88% of the individuals possessed fructose, glucose, sucrose and maltose, and 63% of then additionally possessed raffinose and/or melibiose. 6. Judging from the appearance rate of fully nectar-sucked individuals among those coming for blood sucking, the diurnal activity of nectar-sucking in T. iyoensis, T. sapporoensis, T. humilis and T. rufidens seemed to be parallel to the blood-sucking activity. 7. Comparison of nectar-sucking between the autogenic T. iyoensis and strongly blood-sucking (anautogenic) T. chrysurus revealed that there was little difference in the rate and degree of nectar-sucking as well as the composition and concentration of sugars. A significant difference was observed only in the distribution of nectars after ingestion, that is, in T. iyoensis nectars were detected also in the midgut. This seemed to be a distinctive character of the autogenic species, since the same distribution pattern was observed also in T. sapporoensis and T. rufidens, which belong to the same autogenic species group.
