Biochemical and physiological studies of certain ticks (Ixodoidea). Qualitative and quantitative studies of hemocytes.

Abstract

Qualitative and quantitative studies were made of the hemocytes of 4 tick species from 2 genera representing the 2 principal tick families: Hyalomma anatolicum excavatum Koch and Hyalomma dromedarii Koch (Family Ixodidae), and Argas ( Persicargas ) persicus (Oken) and Argas ( Persicargas ) arboreus Kaiser, Hoogstraal & Kohls (Family Argasidae). The hemocytes were studied from laboratory-reared ticks representing various nutritional states and developmental stages, and both sexes of each species. Hematocrits and total hemocyte counts gave the highest values in unfed adults. Hemocyte numbers decreased during engorgement and continued to fall in the ixodids after dropping from the host; however in argasids counts were slightly increased during this period. Neither sex nor species influeneed the hematonits and total hemocyte counts. The hemocytes were classified into 3 major categories based on Giemsa-staining properties: prohemocytes, plasmatocytes, and spherule cells. The latter 2 categories were subdivided into early and late forms on the basis of extent of vacuolation and spherule density, respectively. Mitotic figure and binucleated cells were also observed. No granular hemocytes were found. Supplementary observations were made with supravital staining and with phase contrast. All cell types appeared to be structurally uniform in the 4 tick species studied. Differential hemocyte counts showed that plasmatocytes accounted for a larger portion of the total cell population than than the other 2 basic types. Values for argasid plasmatocytes were 1.5–2.0 fold greater than for counterpart ixodids. In ixodids the relative proportion of early and advanced forms shifted toward the advanced form as the tick passed through the hunger, engorgement, and preoviposition states. Prohemocyte counts were highest in unfed adult ixodids. Spherule cell numbers increased about 2 fold with engorgement of ixodids but were considerably reduced in argasids. Mitotic figures did not exceed 1.2% and binucleated cells 0.32% of the total cell population. These 2 forms were usually found together, most notably in premolt third nymphal instars and in unfed adults. Change in nutritional state had a greater influence upon the differential hemocyte count than did change in sex, species, or genus.