Research into the relative importance of Tabanidae (Diptera) in mechanical disease transmission. II. Investigation of the behaviour and feeding habits of Tabanidae in relation to cattle

In this second paper on Tabanids in Tanzania [cf. preceding abstract], observations made over a period of 3 years on the behaviour and feeding habits of Tabanids on a dairy farm near Dar es Salaam are reported. Tabanus biguttatus Wied., T. fraternus Macq., T. taeniola P. de B., T. gratus Lw. and Haematopota decora Wlk. were studied while the cattle were resting from 10.30 a.m. to 3 p.m. in a holding pen partly covered by a roof, and the findings were supported by observations on restrained animals 40 m away from the herd and by the dissection of 11 189 flies to determine the presence and size of fresh blood-meals. Relation of the findings to the principles of mechanical transmission showed that the small species T. gratus and H. decora did not behave in the way expected of potential vectors of disease agents. Of the large species, T. biguttatus and T. fraternus did not show the expected feeding habits. Individual blood-meals taken by these species varied in size, and the observations suggested that a considerable time might elapse between interruption of feeding and its resumption in this species. T. taeniola, on the other hand, was aggressive, and flies deliberately disturbed during a meal immediately made determined efforts to resume it. The flies were replete within 1-3 min. Blood-meals of this species showed little variation in size, confirming its determination to engorge completely and, when disturbed, to continue feeding within such a short time that an appreciable number of flies containing the first part of a meal could not be caught. It is concluded that T. taeniola fulfilled all requirements for mechanical transmission of disease under natural conditions.