Resource regulation by a stem-galling sawfly on the arroyo willow.

Examines the tenthredinid sawfly Euura lasiolepis on Salix lasiolepis. Normally, as willows age they become less susceptible to galling, but heavy Euura galling maintains willows at a young, relatively susceptible juvenile stage. The Euura form more galls on long shoots. Long shoots are found on clones with young branches. Heavy galling stunts or kills growth distal to the gall, stimulating sprouting by indefinitely dormant buds located near branch bases. The resulting young branches keep the clone susceptible to further galling. Increasing branch age of lightly galled clones confers resistance to galling. -from Authors