5: Diet preference and requirements shift throughout ontogeny in the South American locust (Schistocerca cancellata)

Generalist feeders often behaviorally regulate their food choice to achieve their preferred macronutrient ratios to enable maximal growth and survival. However, the vast majority of studies on the topic have examined only a small portion of animal ontogeny, and it is not clear whether preferred ingestion ratios of protein:carbohydrate (P:C) intake targets (IT) vary during development of insects and other animals. Locusts and grasshoppers have been extensively used as models to study P:C IT, and these have generally found that ITs during the final instars and young adults showed balanced or carbohydrate-biased ITs. To understand the nutritional requirements during ontogeny, we measured the IT of each instar of the South American Locust, Schistocerca cancellata. In addition, we recorded development performance and survival of locusts reared on single artificial diets varying in P:C for the entire developmental period. In order to assess survival on different P:C diet, once each week we counted the number dead individuals of each sex and diet treatment. In contrast to studies focused on only the final instar, across the entire development period, performance (assessed as mass gain, survival, and rate of development) was highest on protein-biased artificial diets. Most instars chose protein-biased diets while only the final juvenile instar and adults chose carbohydrate-biased diets. We conclude that both dietary preferences and macronutrient needs of S. cancellata change dramatically during ontogeny, and that studies of the final instar are inadequate to predict nutritional needs throughout development. Supported by NSF IOS-1826848 and BARD FI-575-2018.