To determine whether relative enrichments of 15N and 13C in locusts are influenced by diet, locust nymphs were raised from hatchlings to adults on either seedling wheat or maize. Maize provided less hexose sugars and protein per gram than did wheat. Maize also depends on the C4 form of photosynthesis, while wheat uses the C3 form; this difference in photosynthetic pathways produces two distinguishable ranges of 13C values.The lower-quality maize diet corresponded to a 5.1 increase in animal 15N, relative to diet, whereas the wheat diet corresponded to an increase of only 2.3 . The maize-fed animals were more 13C-depleted in lipid, trehalose and chitin than those fed wheat. The results for 15N and 13C suggest that substrate recycling occurred on the low-quality maize diet. Consequently, we examined the variations in the isotopic differences between locusts and their diet at the biochemical level.