Abstract: The pine sawyer, Monochamus alternatus (Coleoptera: Cerambycidae), is the most important pest of pine Pinus massoniana throughout China. In this study, the parasitoid Dastarcus helophoroides (Coleoptera: Bothrideridae) eggs and adults were released in six plots of the pine forests for controlling M. alternatus. The control effect was evaluated by two indexes, i.e., infested trees number and the pest larvae number in a host tree. Meanwhile,the parasitism rate of this parasitoid to its host was measured in indoor mesh and field mesh. Results showed that, releasing both eggs and adults was able to effectively control M. alternatus. In three plots of releasing the parasitoid eggs, the mean adjusted reduced rate of the pine sawyer larvae per tree was 48.54%, and the mean adjusted reduced rate of infested trees was 63.07%. In three plots of releasing the parasitoid adults, mean adjusted reduced rate of the pine sawyer larvae per tree was 47.00%, and the mean adjusted reduced rate of infested trees was 68.00%. The controlling effects by releasing adults of the parasitoid were a little better than that by releasing eggs of the parasitoid, without significant difference between them. The parasitoid responded differentially to DBH of 5-8 cm, 10-15 cm, or >18 cm pine sawyer-infested cutlogs. The highest parasitism rate was 72.41% in DBH of 5-8 cm cutlogs, significantly higher than the others. During three periods (May, July, September) of releasing the parasitoid, the parasitism rates of the pine sawyer larvae orderly were 68.50%, 21.63% and 30.29%, respectively. These findings determined that controlling larva of M. alternatus by releasing D. helophoroides to the forest in May was feasible, which is a new technology in biocontrol method.

Key words: Monochamus alternatus, Dastarcus helophoroides, field control effect, biocontrol, Pinus massoniana