The ultrastructure of the cuticle and sheath of infective juveniles of entomopathogenic steinernematid nematodes

Abstract

AbstractThe ultrastructure of the cuticle of infective juveniles (IJs) ofSteinernema carpocapsae(newly emerged and 80-day-old) and newly emerged IJs of S.riobravis, S. feltiaeandS. glaseriwas examined using transmission electron microscopy. The thickness of four distinctive layers of the cuticle was measured: epicuticle, cortical and median layer, striated layer and fibrous mat. The thickness of the cuticle was correlated with the size of the IJ. In the case of newly emerged IJs, the smallest species,S. carpocapsae, had a cuticle thickness ofc.270 nm compared withc.460 nm forS. glaseri, the largest of the four species. The overall thickness of the cuticle or the thickness of the cuticle layers was not correlated with the ability of the IJs of the four species to survive desiccationper se.The major difference between newly emerged IJs of the four species was thatS. carpocapsaehad a proportionately thicker striated layer compared with the other three species. The significance of this is not known but it may be an adaptation involving the nictation behaviour of this species. A substantial change was observed in the cuticle of aged (80-day-old) IJs ofS. carpocapsae, whereby the thickness of the cortical and median layer increased by more than 100% and the overall thickness of the cuticle increased by about 50%. Two possible explanations for this increase are: (i) new material was synthesized; or (ii) the fluid content of this layer increased due to an increase in the permeability of the outer layers of the cuticle. The ultrastructure of the sheaths ofS. feltiaeandS. glaseriwas also examined and, apart fromS. glaserihaving a thicker sheath, the structure of the sheath in both species was similar, with the epicuticle and striated layer still visible.