Monitoring of sawfl y ( Hymenoptera: Tenthredinidae Hymenoptera: Tenthredinidae ) infestation on spruce

A new method for evaluating damage caused by tenthredinids to Norway spruce stands is based on defoliation of the top whorls. A scale with four classes of defoliation was established that is easy to use. Defoliation can be displayed graphically on a grid map (Central European system), in which the map fi elds are delimited by parallels of latitude (6 by 6 minutes) and meridians (10 by 10 minutes) with an approximate size of 11.2 × 12.0 km. The degree of defoliation for an entire forest can be marked by circles of different size in the map field. The range and intensity of an infestation, and the change in defoliation from year to year are easily seen.