Abstract: In order to evaluate the control effects of Sclerodermus sp. (Hymenoptera: Bethylidae) on the 3rd instar larvae of Monochamus alternatus (Coleoptera: Cerambycidae), a method of functional response was used to test the effects of preying on hosts and parasitization, and the density effect of Sclerodermus sp. was also studied. The results showed that when the density of the bethylid wasps was 1 per cylinder, the functional response of Sclerodermus sp. preying on the 3rd instar larvae of M. alternatus could be described by Holling Ⅱ model. The maximum quantity of hosts killed by preying on hosts by one bethylid wasp was 9.48, and the average value was 3.75. The functional response of parasitization fitted Holling Ⅰ model, in which the threshold limit of the number of hosts is 4. The searching effects of preying on hosts and parasitization attenuated linearly with the increase of host density. When the density of M. alternatus larvae was 30 per cylinder, with the density of wasps increasing, the functional response of parasitization and preying on hosts increased linearly while the searching effect attenuated. A model between ratio of bethylids to beetle larvae and total lethality showed that when the ratio of the bethylids to larvae was 0.9805 (approximately 1∶1), the mortality of M. alternatus larvae was the maximal. The results suggest that Sclerodermus sp. is an effective natural enemy to M. alternatus larvae. This study provides essential data and methods for evaluating control ability of Sclerodermus sp. on M. alternatus, and also supplies theoretical basis for its release amount in the field.

Key words: Sclerodermus sp., Monochamus alternatus, preying, parasitization, functional response, searching effect, density effect