Effectiveness of Torymus (Syntomaspis) sinensis, an imported parasitoid of the chestnut gall wasp

1982年在熊本县大津板栗园释放的副寄生蜂Torymus(Syntomaspis)sinensis的种群数量长期处于低密度状态，但自1992年以来有所增加，因为它的性别比在前一年有所改善。但在1995年，栗小蜂的寄生率仅为28%。为确定熊本市栗小蜂种群增长延迟的季节，于1994年和1995年在茨城县3个栗园进行了调查，寄主小蜂已被控制在低密度水平。与熊本市的结果进行比较，结果表明，熊本县的成虫死亡率和兼性重寄生蜂的重寄生率存在显著差异，熊本市的死亡率和重寄生率均显著高于茨城。5种兼性重寄生寄生蜂侵染白纹伊蚊T.(S.)测定了中华按蚊幼虫的种类：日耳菊(Torymus(Torymus)geranii)、布氏真姬蜂(Eurytoma Brunniventris)、七翅真姬蜂(E.setigera)、乌罗非鱼(Eupelmus Urozonus)和真姬蜂(Eupelmus sp.)其中，真姬蜂Eupelmus spp.和圆尾真姬蜂E.setigera在熊本中占有重要地位。和一种亲缘关系较近的寄生蜂T.(S.)从初夏到秋季，甜菜夜蛾表现出较长的滞育。为了确定解除滞育的条件，用滞育的成熟幼虫进行了初步试验。从田野上采集的中华龙虾。结果发现，即使在15ﾟ℃下，10ﾟ℃的低温也能打破幼虫的滞育。解除滞育后，幼虫在10ﾟC条件下仍发育为成虫。因此，试验应控制在5、10和15ﾟC的条件下，以5、10和15天为周期，以20或25ﾟC为周期来确定解除滞育条件。

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.