Effects of ascorbic acid deficiency on growth and cuticle composition of Manduca sexta and Spodoptera littoralis

Abstract

Immediately following the withdrawal of ascorbic acid from the diet of Manduca sexta, the larvae increased food consumption, accumulated tissue water, voided drier faecal pellets and their growth rate declined. As a consequence of general debilitation of body fat and muscle, larvae suffering from inanition, contained a high proportion of their body weight as exoskeleton which had abnormal ash and moisture content and reduced load bearing capacity. Cuticle lipid decreased from 6.6 to 1.1% and levels of bound hexose were also reduced from 292 to 113 μg/mg. The normal complement of structural proteins was greatly reduced in guanidine and acid-soluble collagenous protein. Similar reduced recoveries characterized ascorbic acid deficiencies in Spodoptera littoralis larvae with additional redistribution of the NaOH-soluble polypeptide fraction. At the onset of pupation, deficient S. littoralis failed to extend the sclerotized regions of the wing pockets such that a portion of untanned abdomen was visible. The degree of exposed abdomen was inversely proportional to the ascorbic acid supplement. The rapidity of the onset of symptoms in phytophagous lepidoptera, a taxonomic group of low collagen content and exceptionally high ascorbic acid dependency, is in keeping with severe disruption of ion and fluid transport mechanisms rather than in deficient hydroxylation characteristic of vertebrate scurvy.