Assembly, mating, and energetics of Hybomitra arpadi (Diptera: Tabanidae) at Churchill, Manitoba

The mating system of H. arpadi was studied at a subarctic, treeline site near Churchill, Manitoba, Canada. Males aggregated in linear clearings on a hilltop in spruce-larch forest, hovering at a mean height of 13±1.3 (SE) cm. Hovering occurred only on sunny days (_12°C) for periods of up to 11 h. Males oriented parallel to the longitudinal axis of the aggregation site, independent of wind direction or solar azimuth. Few copulations were seen but there was a high frequency of aborted copulations involving nulliparous and parous, con- and heterospecific females. Males that intercepted females were morphologically distinguishable from the remainder of the population on the basis of allometric relationships described by principal components. Aggregating males had highly variable quantities of carbohydrate in the crop, with early-hovering males tending to have the largest quantities; carbohydrate concentration was much less variable. Potential hovering durations estimated from crop energy varied from a few minutes to nearly 5 h, but no individual male had sufficient energy reserves to hover for the entire aggregation period on continuously sunny days. Hovering males maintained a mean thoracic temperature of 40.0°C, as much as 23.5° above ambient. Thoracic temperatures were almost invariant across males and over a wide range of ambient temperatures, increasing only slightly with increasing ambient temperature.