Performance of the tree-feeder Orgyia leucostigma (Lepidoptera: Liparidae) on artificial diets of different water content: A comparison with the forb-feeder Manduca sexta (Lepidoptera: Sphingidae)

Abstract

The egg-to-pupa growth rate of Orgyia leucostigma, which normally feeds on tree foliage, is an order of magnitude smaller than that of Manduca sexta, which normally feeds on herbaceous foliage, on four different nutrient-rich artificial diets. Relative growth rates of fifth-instar female O. 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 O. 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 contributing most to the efficient retention and use of water by larvae of both species on low-water diets 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.