Hematophagous activities of Hybomitra laticornis and H. tetrica rubrilata (Diptera: Tabanidae)

After a review of the literature on the quantity of blood taken and rapidity of ingestion by tabanids, an account is given of observations on the feeding behaviour of Hybomitra laticornis (Hine) and H. tetrica rubrilata (Philip) that were undertaken in New Mexico as part of a study on tabanid transmission of a filarial parasite, Elaeophora schneideri. It was found that a female of H. laticornis required about 20 s to become fully engorged, from the time that it landed on the host and began to probe with its mouthparts for a suitable feeding site. Flies fed to engorgement unless forcibly disturbed, in which case they circled round the host and resumed feeding after a short time. Engorged flies that were not captured glided to a tree and apparently experienced difficulty in flying.On the mule and the horse that were mostly used as hosts, most flies were collected from the ventral part of the neck, in front of the shoulder, on the inner side of the hind legs, and from the ventral side of the thorax and abdomen, and these flies engorged more rapidly than those feeding on other parts. In observations on tame mule deer (Odocoileus hemionus), feeding occurred mostly on the bridge of the nose. The amounts of blood taken were 0.08-0.18 ml by H. laticornis and 0.1-0.2 ml by H. t. rubrilata, a larger insect. It was calculated that the potential rate of blood loss would be 0.5 litre in 8 h, although in natural conditions with a freely mobile host the actual rate would probably be much less. Calculations on the rate of blood digestion led to the conclusion that these tabanids fed every 4-5 days, although in the field some flies appeared to take a second blood-meal before the first was completely digested. No positive correlations were detected between fly abundance and weather conditions, except that maximum activity occurred at 20-32 deg C and 17-42% RH.