The nutritional significance of sterol metabolic constraints in the generalist grasshopper Schistocerca americana

Sterols are essential nutrients for grasshoppers, as well as all other inse cts, but metabolic constraints can limit which phytosterols support normal growth and development. In the current study, the generalist grasshopper Sc histocerca americana was used to address two questions related to grasshopp er sterol nutrition: (1) how does sterol quantity influence growth and surv ival, and (2) how do mixtures of suitable and unsuitable sterols at differe nt concentrations influence growth and survival? Results from the first exp eriment indicated that this grasshopper species had a minimum sterol requir ement of 0.05% dry weight; as sterol quantity increased above this concentr ation, however, survival and performance were not enhanced. Results from th e second experiment revealed two novel aspects of sterol nutrition in grass hoppers: (1) when suitable sterols were limiting, most individuals could no t use unsuitable sterols to meet the minimum sterol requirement (i.e. no sp aring occurred), and (2) above a certain threshold, unsuitable sterols were deleterious even when suitable sterols were present at a concentration tha t alone permits normal growth and development We discuss these physiologica l findings in terms of how sterol metabolic constraints in grasshoppers mig ht influence foraging. (C) 1999 Elsevier Science Ltd. All rights reserved.