GLYCINE IN DIGESTIVE JUICE - A STRATEGY OF HERBIVOROUS INSECTS AGAINST CHEMICAL DEFENSE OF HOST PLANTS

A large amount of free glycine was found in the digestive juice of sev eral Lepidoptera larvae and appears to be secreted. The amount of glyc ine differs greatly among species and seems to correlate with the host plant. Several species of Lepidoptera from different families which f eed on the privet tree, Ligustrum obtusifolium, show extremely large a mounts of free glycine. The concentration of glycine reached 57 mu mol es/g (0.4%). The leaves of the privet tree have an extremely strong pr otein denaturing activity, enough to make protein completely nonnutrit ive. This denaturing property closely resembles the activity of polyph enolics, digestion inhibitory compounds common among plants. In vitro studies showed that free glycine completely inhibits the denaturing ac tivity of the privet leaves. These results suggest that insects secret e glycine to counter the chemical defenses of host plants. (C) 1997 Pu blished by Elsevier Science Ltd.