A Study on the Biology and Ecology of the Larch Sawfly Pristiphora erichsonii and Its Control

Pristiphora erichsonii(Htg.)has one generation a year in Beijing area with prepupae overwintering in cocoons in the litter and soil under the tree crown. The effective accumulative temperature for the eggs and larvae was studied by means of linear regression method,which were 110.4586 and 383.5238 day·degree. The optimal developmental tem-perature for larvae ranges from 16～20℃. The average number of egg mass per twig is 0.73 at the border of the larch forest or at the western and northern part of the tree,while 0.3 per twig inside the forest or at eastern or southern part of the trees. The parasitic rate of co-coons reached 83.23%. The effects of abiotic and biotic factors on its occurrence were discussed. According to the results from indoor and field control experiments using Beauveria,B. t.,and netomopathogenic nematodes as control agents, it is assumed that the enmatodes are the best biocontrol agents which can infect the larvae on the trees and mature larvae on the ground with a mortality of 80%～100%. The mortality caused by Beauveria and B. t. are 28%～52%and 5%～27%,respectively, with a mortality as high as 98%～100%,Dimilin is also a good insecticide to control the sawfly.