Freeze-fracture characteristics of insect gustatory and olfactory sensilla. II. Cuticular features

The freeze-fracture technique has been used to obtain detailed information about cuticular constituents and outgrowths of the external skeleton of labella and antennae in the bluebottle fly Calliphora vicina and the antennae of the small moth (Yponomeuta spp.). The lamellated exoskeleton has a fibrous endocuticle and an exocuticle lacking fibers. Ductuli connecting the inside of the animal with the outside run perpendicularly through the endocutile and at angles of up to 45° in the exocuticle. Skeletal outgrowths lack fibers and display fracture features similar to those of the exocuticle. Among those having neuronal endings, gustatory, olfactory, and tactile hairs can be recognized. Noninnervated outgrowths can be subdivided into scales and pseudotrichia. Criteria such as shape, length/width-ratio of hairs, texture, presence and place of pores, shape of pores, and form of the socket or base are presented for further classification. Cuticular features of single-walled olfactory hairs of Calliphora are compared with those of several other species. Based on the shape of the pores, five types of hairs can be distinguished using literature data. It is concluded that the freeze-fracture technique is a valuable tool with which to describe the microarchitecture of the insect exoskeleton and supplements scanning electron microscopy, which is useful for describing the overall skeletal features.