Abstract: Anoplophora glabripennis (Motsch.) is a main wood borer of willow, poplar and other deciduous hardwood trees in the northwestern China and North China. It is difficult to control this insect pest.  Dastarcus helophoroides (Fairmaire) is an important parasitoid of A. glabripennis and other cerambycids, and it has been used as a biological agent to control A. glabripennis in recent years in China. However, due to long life-span of D. helophoroides and its hosts, the evaluation of biological control effect of D. helophoroides remains a challenge. In order to appropriately evaluate the biological control effect of A. glabripennis by D. helophoroides, field experiments of three consecutive years were carried out to investigate the control effect after releasing the parasitoid. The sample area was located in Weiyang District, Xi’an City, northwestern China, where Salix babylonica L. was seriously infested with A. glabripennis. The parasitoid release site and two control sites were selected in this area, of which one control site (control site 1) was adjacent with the parasitoid release site, the other control site labeled as control site 2 was 1.5 km away from control site 1. All trees in the sample sites were painted and marked with numbers, so they could be continuously investigated in the following years. D. helophoroides adults were released in the releasing site on May 30, 2009. The results showed that the infested rates of A. glabripennis decreased both in the parasitoid release site and in the neighboring control site (control site 1) in the 3rd year. The average numbers of larval frass extruded hole per tree were decreased from 4.63 holes per tree and 5.06 holes per tree, respectively, in 2009 to 0.93 holes per tree and 0.87 holes per tree, respectively, in 2011. The infested rates of A. glabripennis in control site 2 were not significantly different between the first year (2009) and the third year (2011) （P＞0.05）, and the average number of frass holes per tree was 7.41 holes per tree in 2009 and 7.68 holes per tree in 2011, respectively. The results reveal that D. helophoroides can effectively control A. glabripennis and is a prospective insect natural enemy. Finally, methods for evaluating biological control effects of the longhorned beetles in fields were discussed based on the present study. For the longer life-cycle forest insect pests and their insect natural enemies, convincing evaluation results of biological control should be based on survey of longer period on treatments.

Key words: Anoplophora glabripennis, Dastarcus helophoroides, wood borer, insect natural enemy, biological control