The muscles of newly hatched Schistocerca gregaria larvae and their possible functions in hatching, digging and ecdysial movements (Insecta: Acrididae)

Abstract

A detailed study of the hatchling musculature in Schistocerca gregaria (Forskål), and comparison with muscles of older first‐instar larvae and adults, revealed four categories of muscles: those which are present throughout life (permanent muscles), those which are present only in the hatchling and which break down during the first‐instar larval stage (first accessory muscles), those which are characteristic of larvae and break down in the adult (secondary accessory muscles), and those which are rudimentary or absent to start with, becoming functional in the adult. This last group, including the flight muscles and the muscles of the genitalia have not been studied. Of the remainder, the head and legs contain only permanent muscles, the contrast between larvae and adults being in the neck, thorax and abdomen. The positions and possible functions of the two groups of accessory muscles are discussed, particularly in relation to hatching, digging and ecdysis of the vermiform larva, and specific functions of the permanent muscles of neck, thorax and abdomen at this time are suggested, and compared with their better known functions in the fully hardened, free‐living insect.Summary:The study of the musculature of the newly hatched locust revealed not just the normal complement of muscles found in the adult, but batteries of accessory muscles which aid hatching, digging and ecdysial processes. Some of these muscles are attached across and onto the membranous regions and probably prevent ballooning of the intersegmental regions during high pressures, thus ensuring expansion of the presumptive sclerite regions rather than a separation of them.In the abdomen the lack of apodemes, the small overlap of adjacent sclerite regions and the easily distorted cuticle are all factors allowing the external muscles to assist the internal muscles and the accessory muscles in abdominal contraction. Such contractions are required for hatching and digging of the vermiform larva.Special muscles are associated with the ampullae and brustia, which break down during the first instar, while the other accessory muscles persist until the adult stage is reached, and are presumably used at later ecdyses.