A potential influence of rhizobium activity on the availability of nitrogen to legume herbivores.

Evidence is presented which supports the hypothesis that allantoin, a ureide that is a major storage form of nitrogen (N) in legumes whose N is derived from N-fixation, is not utilizable by at least some insect herbivores. We suggest that the nutritive quality of soybean foliage for Mexican bean beetles is influenced by soil nitrogen level through its impact on rhizobial activity which indirectly alters the proportion of ureide-nitrogen to amino acid-nitrogen without affecting total Kjeldahl-nitrogen. This may provide a basic mechanism for protecting the nitrogen stores of legumes from herbivory while avoiding the metabolic burden of secondary compound production.