Abstract: During the study on a biocontrol program by releasing a parasitoid, Sclerodermus pupariae Yang et Yao (Hymenoptera: Bethylidae), for control of Massicus raddei (Blessig) (Coleoptera: Cerambycidae), a wood borer with long generation period and developmental uniformity of Quercus liaotungensis Koidz and Q. mongolica Fischer in northeastern China, it was found that the parasitoid preferred to parasitize the 1st-3rd instar larvae of the pest with high parasitization rate, but not on elder host larvae (over 3rd instars). In order to understand the maintenance of the parasitoid population and whether sustainable control effect after its release, an investigation on alternative hosts of the parasitoid was carried out in oak forests. We found several alternative hosts in the oak trees attacked by M. raddei, including Moechotypa diphysis (Pascoe), Masosa myops Dalman (Coleoptera: Cerambycidae), and Lamprodila virgata (Motchulsky) (Coleoptera: Buprestidae). The parasitoid inoculation test indicated that there were significant differences in parasitism on different potential hosts with the high parasitization rates on both M. diphysis (76.67%) and L. virgata (73.33%). When the bethylid parasitized the four host species above, between them the differences in preoviposition period, number of eggs laid, number of females produced and the emergence rate, body length and life-span in the 2nd generation were not significant, and only the larval and pupal duration as well as the rate of females with wings and the ratio of female to male showed a little difference. The parasitization rates on larvae of M. diphysis and M. myops were higher than those on other hosts, and the biological observation in forests indicated that the larvae of the two cerambycids always existed during the unfavorite developmental periods (i.e., over 3rd instar larval and pupal stages) of M. raddei for the bethylid to parasitize, clearly suggesting that the two cerambycid species are the main alternative hosts of S. pupariae in oak forests. The results of the present study indicated that the biocontrol program using S. pupariae could have sustainable control effects on M. raddei for the bethylid after releasing of the parasitoid, M. diphysis, M. myops and other wood pests can be used as alternative hosts to keep its high population, and when the proper larval stage of M. raddei in the next generation appeared, it could transfer to the main host for parasitization.

Key words: Sclerodermus pupariae, Massicus raddei, Moechotypa diphysis, Mesosa myops, alternative host, parasitization, biology