Attacks of Neodiprion sertifer on Pinus contorta1

Abstract

Neodiprion sertifer, the European pine sawfly, has in the past attacked mainly Pinus sylvestris. Afforestation of areas in northern Scotland with P. contorta in the early 1960s and subsequently has led to widespread outbreaks of N. sertifer on this species, attacks being most severe on trees 5 to 12 years old. The most serious damage is removal of the 1‐year and older needles. Complete loss of this foliage often occurs at the peak of an outbreak. Also, at high population densities, larvae may consume patches of bark, leading to weakening and stem breakage in high winds. Field studies comparing protected (undefoliated) randomized plots of P. contorta with defoliated plots in Shin Forest (Sutherland) were carried out over the 1982–1983 growing seasons. Comparison of leaf/sapwood basal areas in undefoliated and defoliated plots indicated losses of up to 27% of total leaf area, both removal of old foliage by larvae and a reduction in current‐year foliage being involved. Further, there were significant reductions in sapwood basal area and height increment between control plots and some of the defoliated plots. The impact of such defoliation is to prolong the rotation by approximately 2 years.