|Budget Amount *help
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1992 : ¥200,000 (Direct Cost : ¥200,000)
Fiscal Year 1991 : ¥400,000 (Direct Cost : ¥400,000)
Fiscal Year 1990 : ¥1,400,000 (Direct Cost : ¥1,400,000)
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.