Technique for age-grading late third-instar Hypoderma lineatum (Diptera: Oestridae).

Three developmental phases are described for age-grading third-instar Hypoderma lineatum (Villers) based on color and development of the posterior spiracles. Early Phase 1 (P1) larvae are white in appearance, and their kidney-shaped posterior spiracular plates have no melanization. By the end of this phase, the cuticle has become yellow, and the margins of the spiracular plates begin to melanize. The cuticle of P2 larvae continues darkening from yellow to tan to light brown and is accompanied by a progressive melanization of the spiracular plates. The third phase, P3, has a cuticle that is not black like larvae that are ready to emerge from the hides for pupation, but the posterior spiracular plates are fully developed and melanized without a space between the two plates.