The relationship between diet and the size of the midgut caeca in grasshoppers (Insecta: Orthoptera: Acridoidea)

A survey of the size and form of the midgut caeca in relation to diet has been carried out on 173 species from 21 families and subfamilies of Acridoidea (grasshoppers). Although differences exist in the size of the anterior caecal arms relative to body length, these differences are not related to the type of food eaten. Assuming that the anterior arms have a key role in digestive and absorptive processes, this suggests that different foods make similar demands on these processes. The posterior caecal arms are smaller in graminivorous species than in species eating other types of plants as a whole or part of their diet. This is true across all the taxa, including those families and subfamilies that are predominantly forb-feeding. It is suggested that the posterior caecal arms have a special role in the detoxification of plant secondary compounds and that the requirement for this is reduced in graminivorous species because of the lower levels of toxic secondary compounds in grasses. A specialized pocket region is present in the posterior caecal arms of some forb-feeding species. Its occurrence across the taxa is spasmodic. It may be concerned with the removal of phenolic compounds.