Meeting Abstract
Herbivores are often thought to be protein-limited; however, recent studies with locusts have suggested that outbreaks may be facilitated by high carbohydrate food. In this study, we examined dietary preferences and performance consequences of different dietary protein:carbohydrate (P:C) ratios on South American locusts (Schistocerca cancellata) in Paraguay. Marching nymphs (4th and 5th instars) in the field and during lab choice experiments strongly preferred high carbohydrate diets. Single artificial diet experiments showed that survival improved as P:C decreased, despite that mass-specific consumption and growth rates did not vary. Nymphs showed lower survival on local plants compare to artificial diets, suggesting many of the available plants were poor quality food. Locusts given a choice of seven local plants showed a clear preference for one grass species, which had the highest carbohydrate content and carbon to nitrogen ratio. This grass was also the only plant on which the nymphs gained body mass during single-plant feeding trials. Total body lipid content increased as the P:C ratio of the artificial diet decreased. The lipid contents of field marching nymphs were low and similar to those fed 1:1 or higher P:C artificial diets. In summary, foods with high carbohydrate and low protein (low P:C) benefited late instar nymphs by increasing survival and fuels for adult migration. It is plausible that the population growth and ecological success of S. cancellata is at least partially constrained by carbohydrate availability in Paraguay. This research was supported by NSF IOS-1826848 and BARD FI-575-2018.
