A scanning electron microscope study of the developing embryo of Manduca sexta (L.) (Lepidoptera : Sphingidae)

Abstract

Scanning electron microscopy of the developing Manduca sexta (Lepidoptera : Sphingidae) embryo reveals that the body wall of the insect undergoes considerable morphogenesis beginning at 20 hr post-oviposition. The elongated 19 hr embryo contracts in length, which gives rise to the formation of rudimentary segments. By 33 hr, many of the appendage anlagen are visible, the presumptive spiracles appear as bifurcate pits and the proctodeum begins invagination. During this same period, prior to katatrepsis, the body walls become established, and the segments and appendages develop. Between 50 and 60 hr post-oviposition, involution of the oral cavity and reorientation of the associated gnathal appendages occurs. During this same period, katatrepsis and provisional dorsal closure take place. Developmental polarity is evident as a distinctive wave of specialization proceeding posterior to anterior in the thorax/abdomen, and anterior to posterior in the head. Configuration of the oral cavity is strikingly prognathous until just prior to eclosion. Two embryonic molts are apparent, as determined by the remnants of ecdysed “embryonic cuticles”.