Isotopes as host blood markers to measure blood intake by feeding ticks (Acari: Ixodidae).
We have modified an experimental technique in which two different isotopes (Cr51 and I125) were used simultaneously as blood markers for determining the amount of blood removed by feeding ticks. This method enables us to measure separately and directly the volumes of red blood cells and plasma in ticks and to calculate the ratio between the two parameters (concentrating ability). The concentration of red blood cells in nymphs of Amblyomma hebraeum Kock and Rhipicephalus appendiculatus Neumann and in females of these species plus in those of Hyalomma truncatum Kock were found to be twice the amount measured in the labeled blood of goats. Concentrations of plasma in the ticks were approximately two-thirds of that measured in samples taken directly from these same goats. Small nonsignificant differences between the ability of various tick species to concentrate red blood cells and dilute host plasma were found. The advantage of this method is compared with that of the colorimetric and gravimetric methods, and its potential use is discussed.