| Popis: |
The 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. Key Word Inakx: Tobacco hornworm, Manduca sexfa, white-marked tussock moth, Orgyia leucostigma, growth, nutritional indices, water budget, uric acid production, respiration rate, metabolic rate, adaptation to water stress |
