Relationship between feeding, mating, vitellogenin production and vitellogenesis in the tick Dermacentor variabilis

Anti-vitellin IgG directed against Dermacentor variabilis egg vitellin was used in sodium dodecyl sulfate polyacrylamide (SDS-PAGE) gradient gel immunoblots to detect the presence of vitellin and its precursor, vitellogenin, in the organs of feeding adults and in the immature stages of this tick. Vitellin polypeptides were found in the egg, larvae, nymph, and in the unfed adult stages of both sexes. Vitellin polypeptides were first detected in the ovary of mated females during the rapid-engorgement feeding period. These polypeptides were also present in the ovaries of ovipositing females, unmated females fed for extended periods, and fed unmated females that were detached from the host and held for 12 h before dissection. The same anti-vitellin antibody was used in immunoblots to monitor the appearance of vitellogenin in the organs and hemolymph of female ticks. Immunoreactive peptides of vitellogenin were found in the fat body, midgut, and hemolymph of pre-rapid-engorging mated and unmated females. These polypeptides were not found in fed males nor in Malpighian tubes of feeding or ovipositing females. Our data supported the following conclusions: 1) presence of immunoreactive vitellogenin in the adult female fat body, hemolymph, and midgut was dependent upon feeding; 2) in mated feeding females, we could not detect the uptake of vitellogenin by the ovary until rapid engorgement; 3) in unmated females, vitellogenesis did not begin unless prolonged feeding occurred; and 4) during the early developmental stages of this tick, vitellin served as an embryonic nutrient reserve and as a reserve against starvation between feedings.