Distribution of pine shoot beetle attacks within the crown of Scots pine.

Abstract

The seasonal and spatial distribution of pine shoot beetle attacks was studied at Simonstorp in southern Sweden. Scots pine of 15-46 years age and 4-14 m height were felled during the period 1972-1974. Samples of attacked shoots were also collected from standing pines of about 2-3 m height. In 1974, attacks were also counted and labelled individually on preselected pines throughout the growing season. The results indicate a seasonal change in the age distribution of attacked shoots. The average diameter of damaged shoots was about 4.5 mm, ranging from 2 to 6 mm. The spatial distribution of attacks coincided with the distribution of suitable sized shoots, but the attack pattern was modified by the density of attacks per tree. Multiple attacks were frequently observed which indicated a relative shortage of suitable shoots, especially in upper whorls. More than 50 % of all current shoots were affected in upper whorls, whereas a far smaller proportion of the shoots was damaged in lower whorls