Assessing diet quality in free-ranging grasshoppers by frass N content and respiratory quotient

From laboratory studies with several species of grasshoppers and locusts, it has been shown that, given a choice, grasshoppers will self-select a diet with a particular ratio of protein to carbohydrate that provides for optimal growth and development. It is not known to what extent grasshoppers foraging under natural conditions are able to achieve their target intake of protein and carbohydrates. This study explores the use of N content of frass and respiratory quotient to estimate protein:carbohydrate intake of grasshoppers under natural conditions. Calibration was done with natural foods and artificial diets. Preliminary analyses suggest that Melanoplus borealis in Alaska are able to meet their intake target when foraging under natural conditions.