Abstract:

Objective: The present study aims to investigate the adult emergence relationships between Dastarcus helophoroides and its host Monochamus alternatus in Pinus massoniana forests. The result would provide valuable information for applying the parasitoid to control the cerambycid beetle M.alternatus. Method: The adult eclosion and emergence regularity of D. helophoroides and M. alternatus was investigated by releasing D. helophoroides eggs on the M. alternatus larvae and pupae of the infested bait-trees. The flight seasonal dynamics of D. helophoroides and M. alternatus adults was monitored using M. alternatus pheromone lures in the pine forests from 2016 to 2017. The distribution characteristics of D. helophoroides adults on pine trunks were surveyed by dissecting the dead pine trees. Result: D. helophoroides adults could mate and lay eggs soon after overwintering. The overwintered adults of M. alternatus emerged in early May,and disappeared in early July with the peak in late May. The first generation of D. helophoroides adults emerged around late June and early July,and disappeared in late July; the peak of emergence was around early and mid July,which was 42-50 days later than that of the overwintered M. alternatus adults; and the average emergence period and the peak emergence duration were 30.5 d and 11.5 d,respectively. The M. alternatus adults were caught from late April to late October,and the high occurrence period was from late May to late July with the peak in mid June. The D. helophoroides adults could be caught by the M. alternatus pheromone lures from early May to mid October. Approximately 6.62% of the total number of the beetles were caught from May to June. The number trapped increased significantly in July,and reached the peak period in September,which was about three months later than that of M. alternatus adults trapped; Around 93.38% of the total number were caught from July to Octobert. The D. helophoroides adults were mainly distributed in the middle and upper parts of the dead tree trunks,with the upper part accounting for 77.12% of the total. The number of the boring holes by M.alternatus larvae were 55.33% distributed in the upper part,and 37.18% in the middle,and only 7.49% in the lower part. Conclusion: The D. helophoroides adults enter the breeding season soon after overwintering,which makes the larval emergence period of the first generation D. helophoroides coincide with the optimum pupa stage of M. alternatus,which is the result of a long-term co-evolution of the two species. It is indicated that D. helophoroides could be an obligate parasitoid of M.alternatus. The M. alternatus adults of overwintered generation emerge after May,then emigrate to healthy pine trees for feeding and lay eggs later on the harmed trees. The D. helophoroides adults of the first generation emerge after June,then migrate and transfer to the newly-died wood bored by the M. alternatus larvae of the first generation. The parasitoid adults are mainly distributed in the middle and the upper part of the dead tree trunks,and the distribution pattern coincides basically with that of M. alternatus larvae. It could be concluded that the D. helophoroides adult has a significant tracking and following effect on its host.

Key words: Dastarcus helophoroides, Monochamus alternatus, emergence, ecological relationships, Pinus massoniana