ISOTOPES AS HOST BLOOD MARKERS TO MEASURE BLOOD INTAKE BY FEEDING TICKS (ACARI, IXODIDAE)

We have modified an experimental technique in which two different isot opes (Cr-51 and I-125) were used simultaneously as blood markers for d etermining the amount of blood removed by feeding ticks. This method e nables us to measure separately and directly the volumes of red blood cells and plasma in ticks and to calculate the ratio between the two p arameters (concentrating ability). The concentration of red blood cell s in nymphs of Amblyomma hebraeum Kock and Rhipicephalus appendiculatu s Neumann and in females of these species plus in those of Hyalomma tr uncatum Kock were found to be twice the amount measured in the labeled blood of goats. Concentrations of plasma in the ticks were approximat ely two-thirds of that measured in samples taken directly from these s ame goats. Small nonsignificant differences between the ability of var ious tick species to concentrate red blood cells and dilute host plasm a were found. The advantage of this method is compared with that of th e colorimetric and gravimetric methods, and its potential use is discu ssed.