Embryo Development and Morphology of the Rocky Mountain Wood Tick (Acari: Ixodidae)

Dermacentor andersoni Stiles embryogenesis was observed using fluorescent and scanning electron microscopy for eggs held under laboratory conditions (25 degrees C and at 93% relative humidity). Early embryonic cell divisions appeared to be synchronous and holoblastic, giving rise to a uniform blastoderm surrounding the yolk. The cells of the blastoderm became concentrated on one side of the embryo, forming the segmented germ band. Distinct opisthosomal and prosomal segment morphologies, which are characteristic of chelicerate embryos, were observed during germ band elongation. Mouth and leg appendages grew from the prosomal segments. As development progressed, the segments were fused into the idiosoma and capitulum of the free-living larval form. An embryo staging system was established based on embryo developmental morphology and the timing of morphogenetic events. The staging system will serve as a basis for future studies directed at understanding morphogenetic mechanisms or for observing the impact of abiotic factors, such as temperature or humidity, on tick development.