Chemical basis of differential feeding behavior of the larch sawfly,Pristiphora erichsonii (Hartig).

The machanisms by which the larvae of the larch sawfly,Pristiphora erichsonii (Hartig), are prevented from feeding on the single needles of the new shoot of tamarack,Larix laricina (DuRoi) K. Koch, were studied. As a result of extensive purification attempts, five deterrent chemicals were isolated and identified. They are: abietic, dehydroabietic, 12-methoxyabietic, sandaracopimaric, and isopimaric acid. These chemicals, particularly the first two, are abundant in mid-July to August in the single needles and, apparently, provide the basis for the deterrency against the larval feeding.