Diurnal activity of Tabanidae based on collections in Malaise traps.

In further field studies on trapping Tabanids [cf. RAE/B 60, 2199, etc.], four Malaise traps baited with carbon dioxide released at 1000 ml/min were operated for 24 h on 4 days in July 1971 in the Delta Branch Experimental Forest, Mississippi. Local sunrise occurred 2-8 min after 6.0 a.m. and local sunset 9-14 min after 8.0 p.m. during the studies. The traps were emptied at hourly intervals from 5.0 a.m. to 10.0 p.m.; one collection was made at the end of the period from 10.0 p.m. to 5.0 a.m., since previous work had shown that Tabanids were not active during this period. The seven species that were caught in sufficient numbers for study of their diurnal activity were Tabanus abdominalis F., T. fuscicostatus Hine, T. lineola F., T. proximus Wlk., T. subsimilis Bellardi, T. sulcifrons Macq. and Chrysops flavidus Wied. All showed a major peak of activity between 6.0 and 9.0 p.m. and varying periods of activity during the morning. The mean hourly activity of each species on three calm sunny days and one windy overcast day is shown in diagrams and discussed. Flight activity was greater on the overcast day than on the others, and the diurnal distribution of activity was different. It is suggested that light intensity influenced the activity of the flies.