Relative growth rates and nitrogen accumulation rates are lower for third-instar ~Uanduca sexta larvae on an artificial diet containing 65% water than on one containing 82% water, due to reduced efficiencies of conversion of digested food and digested nitrogen into larval biomass. Uric acid production is 2.@-2.5fold greater, and non-feeding respiration rates 16.0% higher in the larvae on the low-water diet. Food is the major source of water for the larvae, with metabolic water making only a minor contribution to water input. Faecal excretion is the major avenue of water loss, although a significant amount of water is also lost by transpiration. Larvae from the low-water diet retain and use a higher percentage of the water they gain than larvae from the high-water diet (49.4% vs 41.9%). They produce much drier faeces (48.1% water vs 77.3% water), and, because their tissues are less hydrated (81.3% water vs 88.1% water), they synthesize 70% more new, fully hydrated tissue from a given amount of water than larvae from the high-water diet. We discuss problems involved in the use of determinations of efficiency of conversion of digested food in establishing causal links between diet, growth, and metabolic maintenance costs, and also offer a definition of food processing costs that distinguishes them from metabolic costs attributable to other processes, such as food acquisition, growth, and moulting. We conclude that reduced growth and reduced efficiency of conversion of digested food on low-water diets are due to limitation in the amount of water available for the synthesis of new hydrated tissue, and not to the imposition of higher food processing costs.
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.
egg-to-pupa growth rate of Orgyia leucostigma, which normally feeds on tree foliage, is an order of magnitude smaller than that of Munduca sexfa, which normally feeds on herbaceous foliage, on four different nutrient-rich artificial diets. Relative growth rates of fifth-instar female 0. leucostigma are only 37-53%, and relative consumption rates only 40-50%, of those of comparably sized third-instar M. sexta larvae. Similarly, respiration rates of 0. leucostigma larvae are only 57-68% those of M. sexta larvae of equal size. The water budgets of the two species are very similar, and the two physiological adaptations c,Dntributing most to the efficient retention and use of water by larvae of both species on low-water diel:s are the resorption of water from the hindgut and the tolerance of reduced levels of tissue hydration. These results are consistent with the prediction of Mattson and Scriber that folivores adapted to feeding on nutrient-poor plants have inherently lower growth rates and lower metabolic rates than folivores adapted primarily to nutrient-rich plants, but it is not clear whether the differences reside primarily in behavioural or physiological processes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.