Chemical Basis for Feeding Adaptation of Pine Sawflies Neodiprion rugifrons and Neodiprion swainei.

Larvae of two pine sawflies, Neodiprion rugifrons Midd. and Neodiprion swainei Midd., consume only old foliage of jack pine, Pinus banksiana Lamb., and leave juvenile foliage intact early in the growing season. The chemical basis for this unique adaptation is a feeding deterrent chemical, 13-keto-8(14)-podocarpen-18-oic acid, which was isolated from juvenile foliage. The content of this deterrent chemical decreases as the foliage begins to mature until needles become acceptable to Neodiprion swainei larvae by August (60-day-old foliage) and to second-generation Neodiprion rugifrons by September (90-day-old foliage). The precise timing of larval acceptance of juvenile foliage indicates a highly specific relationship between these insects and their host tree based on the composition of chemicals in the foliage.