Daily and seasonal flight activity of Tabanidae (Diptera) in the North Dakota sandhills.

Hybomitra lasiophthalma and Tabanus similis were studied during 1987 and 1988. Manitoba traps were placed in 2 separate study sites that had previously produced high catches. Traps were monitored and flies removed hourly from dawn to dusk. Other tabanid species trapped in low numbers during this study included Chrysops indus, H. epistates, H. illota and T. atratus. Results showed that H. lasiophthalma was the first tabanid collected in late May during both years. The flight activity increased rapidly and reached a peak approximately 2 weeks after the first occurrence; numbers decreased rapidly thereafter. T. similis first occurred one week after the initial trapping of H. lasiophthalma and peak flight activity one week after emergence. T. similis was the predominant species during most of the summer in 1987. Traps caught predominantly female flies. Both species actively sought blood meals during daylight hours and their flight behaviour indicated a monophasic diel cycle with peak activity between 11.00 and 16.00 h (CDT) on calm, bright sunny days.