SURVIVAL OF PINE SAWFLIES IN COCOON STAGE IN RELATION TO RESIN ACID CONTENT OF LARVAL FOOD

Several experiments were conducted to determine whether the ingestion of diterpenoids (resin acids) by pine sawfly larvae influences the sur vival of postlarval stages. Larvae of two diprionid sawfly species wer e reared on shoots of two Scots pine clones, one with a low (1.5% dry wt) concentration of resin acids and the other with a high (5.2% dry w t) concentration. No significant treatment-related differences were fo und in any of the experiments with respect to (1) resistance against p arasitoids, (2) preference of predatory shrews and carabids, and (3) a pparency of cocoons in the field to predators. A preference of sawfly prepupae to spin cocoon in feces from larvae reared on high resin acid needles was found. Possible explanations for these results are discus sed. Detection of an unknown compound, possibly a breakdown product of the major resin acid in pine needles (pinifolic acid), in prepupae in dicate that resin acids may be metabolized by the sawflies.