栗山天牛天敌花绒寄甲在栎林中的种群保持机制

花绒寄甲(Dastarcus helophoroides)(鞘翅目:寄甲科Bothrideridae)是寄生栗山天牛(Massicus raddei)中老龄幼虫和蛹的重要天敌,但其寄主栗山天牛世代周期长(3年1代)、发育比较整齐,不利于寄生性天敌种群数量的稳定.为了解利用花绒寄甲防治栗山天牛后,其种群能否在栎树林间长期保持较高的种群数量,达到持续控制栗山天牛的防治效果,调查研究了花绒寄甲在栎树林间的转主寄主和种群保持机制.结果表明,在东北辽东栎树干和树枝上除了栗山天牛外,还有其他8种天牛危害:双簇天牛(Moechotypa diphysis)、四点象天牛(Mesosa myops)、中华薄翅锯天牛(Megopis sinica)、锯天牛(Prionus insularis)、双带粒翅天牛(Lamiomimus gottschei)、八字绿虎天牛(Chlorophorus tohokensis)、日本绿虎天牛(C.japonicus)和拟蜡天牛(Stenygrinumquadrinotatum).其中以栗山天牛、双簇天牛、四点象天牛和拟蜡天牛数量较多,而花绒寄甲在辽东栎树干上的垂直分布与栗山天牛、双簇天牛和四点象天牛的垂直分布重叠较多.室内研究表明,花绒寄甲对四点象天牛老熟幼虫的寄生率达到26.67％,对蛹的寄生率达到了43.33％;对双簇天牛老熟幼虫的寄生率达到20.00％,对蛹的寄生率为6.67％.对双簇天牛和四点象天牛在林间的生活史调查和研究发现,花绒寄甲可寄生的这两种天牛的中老龄幼虫和蛹,在花绒寄甲不适宜寄生的栗山天牛幼龄幼虫期大量存在,表明双簇天牛和四点象天牛是花绒寄甲在栎树林中的主要转主寄主.由于这些转主寄主的存在,花绒寄甲在不利于其寄生的栗山天牛卵期、幼龄幼虫期可转移寄生这些寄主,从而在栗山天牛危害的栎树林间保持了较高的种群数量,达到对栗山天牛长期而有效的持续控制效果.

Population-keeping mechanism of the parasitoid Dastarcus helophoroides (Coleoptera: Bothrideridae) of Massicus raddei (Coleoptera: Cerambycidae) in oak forest

Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae) is an important parasitoid of the oak longhorn beetle Massicus raddei (Blessig) (Coleoptera: Cerambycidae) in China. It had a long developmental period needing three years to finish a generation and its generation showed uniformity. The biological character generally was unfavored for its insect natural enemies to maintain relative stable high populations. In order to understand whether the population of the parasitoid D. helophoroides could keep its high level in forests of oak trees (Quercus liaotungenesis Koidz and Q. mongolica Fischer) or not after its releasing in forests, we investigated its potential alternative hosts in northeastern China oak forests. It was found that there were eight species of longhorn beetle species living in the east-Liaoning oak forests besides M. raddei attacking the oak trees. The numbers of four species of the longhorn beetles were predominant in oak forests, i.e. M. raddei, Moechotypa diphysis (Pascoe), Masosa myops Dalman, Stenygrinum quadrinotatum Bates. However, the vertical distributions of M. raddei, M. diphysis and M. myops on the oak trunk appeared as overlapping with the parasitoid D. helophoroides. The inoculating tests indoor indicated that the relative high parasitism rates occured in both hosts of M. myops and M. diphysis, in the former with parasitism rate 26.67% on the last instar larval stage and 43.33% on the pupal stage, and in the latter with 20.00% on last instar larval stage and 6.67% on the pupal stage. The biological observations of M. myops and M. diphysis in forests indicated that the mature larvae of the two cerambycid species existed always in a year during the unfavorable parasitism periods of D. helophoroides on M. raddei, i.e. egg and young larval stages of M. raddei (prior 3rd instar), for the parasitoid to parasitize and to maintain its high population, as well as that the two cerambycid species were the principal alternative hosts of D. helophoroides in north eastern China oak forests. The results of the present study showed evidence of that the biological control program to apply the parasitoid D. helophoroides could reach effective and sustainable control efficiency for the severe damaged wood borer M. raddei after the parasitoid was released. By parasitizing mature larvae of M. diphysis, M. myops and other six species of cerembycids attacking oaks as alternative hosts D. helophoroides could keep its relative high population, and when the proper larval stage of M. raddei (i.e. over third instar larval stage and pupal stage) for its parasitizing occurred, it then could move to the main host, M. raddei, for parasitizing. Thus, the parasitoid has a high potential as an excellent natural enemy to be used in biocontrol program to make the cerambycid under control.