A STUDY ON BIOLOGICAL CONTROL OF THE CHESTNUT GALL WASP

1982年在熊本县的栗树实验园内，输入性栗果瘿蜂（Dryocosmus kuriphilus）被sinymus (Syntomaspis) ensis寄生的比例一直很低，仅为1%。1989年以后，寄生蜂的寄生数量开始增加，到1992年寄生蜂的寄生率也增加到约6%。为了确定寄生蜂种群生长延迟的原因，对本地兼性寄生蜂的有害作用进行了研究。结果表明，该寄生蜂在成熟幼虫期的高死亡率主要是由兼性超寄生蜂Euplemus sp.、Euplemus urozonus和Eurytoma setigera寄生造成的。另一个延迟的原因被认为是由于雌蜂比例低而没有增加已建立的寄生蜂种群，1992年雌蜂比例也提高了66%。对1981年在福冈aburayama山放生的另一个中华仓鼠种群的分散情况也进行了调查。该寄生蜂在福冈县和佐贺县广泛分布，种群数量呈上升趋势。为了评价和预测本地拟寄生蜂对引进拟寄生蜂效果可能产生的影响，在尚未放生中华夜蛾的冈山县和宫城县进行了引进前研究。结果表明，冈山县和宫城县的优势寄生蜂均为有益桃蚜（Syntomaspis），但寄生蜂种类组成比宫城县更为复杂。前者的优势寄生蜂死亡率高于后者。

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.