Insect herbivory on C₃ and C₄ grasses

This study tested the hypothesis that grasses with the C₄ photosynthetic pathway are avoided as a food source by insect herbivores in natural communities. Insects were sampled from ten pairs of C₃-C₄ grasses and their distributions analyzed by paired comparisons tests. Results showed no statistically significant differences in herbivore utilization of C₃-C₄ species. However, there was a trend towards heavier utilization of C₃ species when means for both plant groups were compared. In particular, Homoptera and Diptera showed heavier usage of C₃ plants. Significant correlations between insect abundances and plant protein levels suggest that herbivores respond to the higher protein content of C₃ grasses. δ¹³C values for six of the most common grasshopper species in the study area indicated that three species fed on C₃ plants, two species fed on C₄ plants, and one species consumed a mixture of C₃ and C₄ tissue.