A STUDY ON BIOLOGICAL CONTROL OF THE CHESTNUT GALL WASP

栗瘿蜂对栗瘿蜂的寄生率1982年在熊本县的一个板栗果园释放了中华合盾蚧（Syntomaspis）sinensis，但该寄生蜂的种群数量一直很低，仅占1%。1992年，寄生率也上升到6%左右。为了确定寄生蜂种群增长缓慢的原因，本文调查了本地兼性重寄生蜂的危害作用。结果表明，该寄生蜂在成熟幼虫期的死亡率很高，主要是被兼性超寄生蜂Euplemus sp.，另一个原因可能是由于雌虫比例低，寄生蜂种群数量没有增加，1992年雌虫比例也提高了66%。（S.）1981年在日本福冈县油山释放的中华小食心虫种群也进行了调查。（S.）结果表明，两个县的优势寄生蜂均为惠盾蚧，但冈山的寄生蜂种类组成比宫城复杂。前者优势寄生蜂的死亡率高于后者。

The parasitization rate of the chestnut gall wasp,Dryocosmus kuriphilus by the imported parasitoid,Torymus(Syntomaspis)sinensis has remained low,only 1%,in an experimental chestnut orchard in Kumamoto Prefecture,where the parasitoid was released in 1982.However,the par-asitoid population began to increase after 1989,and the parasitization rate was also increased to ca.6% until 1992.In order to determine the reasons for delay in the population growth of the parasitoid,the detrimental effect of native facultative hyperparasitoids was investigated. As a result,it was suggested that the parasitoid suffered a high mortality during the mature larval stage mainly from the parasitization by three facultative hyperparasitoids,Euplemus sp.,Euplemus urozonus and Eurytoma setigera.Another reason for the delay was supposed that the established parasitoid population did not increased due to its low female ratio,which is also improved as high as 66% in 1992.Dispersion of another T.(S.)sinensis population released at Mt.Aburayama, Fukuoka in 1981 was also investigated.The parasitoid has been dispersed widely in Fukuoka and Saga Prefectures,where the population is increasing.In order to evaluate and predict a possible effect of native parasitoids on the effectiveness of the introduced parasitoid,a pre-introduction study was carried out in Okayama and Miyagi Prefectures where T.(S.) sinensis has not yet been released.As a result,the most dominant parasitoid was Torymus(Syntomaspis)beneficus in both prefectures,but the parasitoid species composition was more complex in Okayama than in Miyagi. Mortality of the dominant parasitoid was higher in the former than in the latter.