|Budget Amount *help
¥1,500,000 (Direct Cost : ¥1,500,000)
Fiscal Year 1995 : ¥400,000 (Direct Cost : ¥400,000)
Fiscal Year 1994 : ¥1,100,000 (Direct Cost : ¥1,100,000)
A population of Torymus (Syntomaspis) sinensis, a paraasitoid released in 1982 at a chestnut orchrd in Ohzu, Kumamoto Prefecture, had been at a low density for a long time, but it has become increased since 1992 because its sex ratio was ameliorated since the previous year. However, the percent parasitism of the chestnut gall wasp by the parasitoid is only 28% in 1995. In order to determine the raeason for delay of the increment of the parasitoid population in Kumamoto, investigations were made in 1994 and 1995 at three chestnut orchards in Ibaraki Prefecture where the host cynipid has already been controlled at a low density by the parasitoid. Comparing the results with those in Kumamoto, it as found that there was a significant differencs between those localities in the mortality of the parasitoid during mature larval stage and the hyperparasitism of the parasitoid by facultative hyperparasitoids ; i.e., both the mortality and the hyperparasitism were significantly higher in Kumamoto than in Ibaraki. Five facultative hyperparasitoids attacking T.(S.) sinensis larvae were determined : Torymus (Torymus) geranii, Eurytoma brunniventris, E.setigera, Eupelmus urozonus and Eupelmus sp. Among them Eupelmus spp.and E.setigera were important in Kumamoto.
Mature larvae of T.(S.) sinensis and a closely related native parasitoid, T.(S.) beneficus show a long diapause from early summer to autumn. In order to determine the condition for breaking diapause, a preliminary experiment was conducted using diapausing mature larvae of T.(S.) sinensis collected from a field. As a result, it was found that a low temperature at 10ﾟC even at 15ﾟC broke the diapause of the larvae. After breaking diapause, the larvae develop to adults even at 10ﾟC.Therefore, it was concluded that the experiment should be made under conditions controlled at 5,10 and 15ﾟC for periods of 5,10 and 15 days to determine the breaking condition and at 20 or 25ﾟC for development.