Abstract
An observation was made on the nectarsucking behavior of the blood-sucking horseflies, Tabanus iyoensis, which were captured by nets at 7 different stations in Toyama Prefecture in 1972 and 1973. 1. Fifty-nine to 97 per cent horseflies of the total population captured were found to have taken nectar before coming for blood-sucking. although the nectar volume in the abdomen differed in individuals, and by captured date, time and station, approximately 14 per cent individuals retained 7μl or more (fully-sucked), 30 per cent from 3 to 6μl (medium-sucked), and 38 per cent only from 1 to 2μl (a little-sucked). The sugar contents of 5μl nectar in the abdoment of the fully-sucked individual, when analyzed either by phenol sulfuric acid- or anthrone-method, were 1.0 to 2.8mg or 20 to 60 per cent in concentration. 2. Six different sugars from mono- to trisuccharide, i.e. fructose, glucose, sucrose, maltose, mellibiose and raffinose, were detected by the paper chromatography. Although the combination of sugars differed in individuals, approximately 60 per cent fully-sucked individuals contained either all 6 sugars or 5 sugars without raffinose or mellibiose. 3. Two peaks of nectar-sucking activity were observed daily. This daily cycle seemed to occur regularly. Nevertheless, a slight change was caused by weather and by the physiological conditions of the horseflies themselves. 4. Comparison of the nectar-sucking behavior between autogenic Tabanus iyoensis and anautogenic Tabanus chrysurus revealed that the former showed 12 per cent fewer individuals in nectarsucking but 3- to 5-fold concentration of sugar in the abdominal contents. Approximately 27 per cent fully-sucked individuals of the former species preserved sugars both in the diverticulum and the midgut, whereas the latter species (also in T. trigeminus) did only in the diverticulum.
