Morphogenesis of Piercing Stylets in Hemiptera

Abstract

This chapter describes how next-instar piercing stylets of Hemiptera develop between molts and how they replace the old stylets, lost during molting. Because the stylets contain epithelium and bodies of neurons in their widened bases and only sensory dendrites in their narrow long shafts, the new stylet cannot grow inside the old one. Instead, next-instar stylets develop within two-layered “retortiform organs” formed by the basal epithelium invaginating into the head cavity. Their development, styletogenesis, generally resembles the development of holometabolan imaginal discs but has unique features. In particular, the cuticle of the new stylet is secreted by parallel long filamentous projections of styligenic cells. Longitudinal sculpture for interlocking between stylets develops along the lines of contact between these projections. Usually the new stylets are passively extracted during ecdysis because their tips are attached to bases of the old stylets. Some Sternorrhyncha with extra-long stylets extract them actively, probably with the aid of the labium. Newly extracted stylets become interlocked into a bundle by pressure from the maxillary plates, labrum, and labium. Hemipteran stylets are not attached to muscles directly and slide into coupling cuticular structures during ecdysis. Stylet development in Thysanoptera may be similar, but its details remain unknown.