Effects of Different Population Levels of the European Pine Sawfly on Young Scotch Pine Trees

Abstract

The larvae of the Europeanpine sawfly, Noediprlonaertifer (Geoffroy), injure their hosts by old-growth defoliation, debarking, and current-shoot girdling. Defoliation is undoubtedly responsible for nearly all the growth oss. Both height growth and radial growth are inversely related to sawfly population levels, but radial growth is affected most, especially at higher population levels. The extent of growth loss is a function of the amount and the rate of foliage removed. Damage after 2 seasons depends upon the quantity of foliage available and removed in both seasons. Trees are seldom without foliage because some new-growth needles appear before all the old-growth needles can be consumed. Even at very heavy population levels defoliation seldom exceeds 90% when old and new foliage are considered together. Since new foliage continues to grow after the sawflies leave the host, the trees "recover" later in the season. Host mortality was not observed even after 3 years of severe defoliation.