The effect of diet water content on energy expenditure by third-instar Manduca sexta larvae (Lepidoptera: Sphingidae)

Abstract

The total energy expenditure during the third instar of Manduca sexta larvae on a diet containing 65% water is substantially higher than that of larvae on a diet containing 82% water. The higher energy expenditure of larvae on the low-water diet is due to (1) a greater amount of time spent in the feeding stage of the instar and (2) to a higher respiration rate throughout the instar. We discuss problems in establishing causal links between diet, water content, growth and energy expenditure, and emphasize that the higher energy expenditure of larvae on a low-water diet is a consequence rather than a cause of reduced growth rate.