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

1982年在熊本县大津县的板栗园内放生的寄生蜂白穗蛾（Syntomaspis）的种群密度长期处于低水平，但自1992年以来，由于性别比例有所改善，白穗蛾的种群密度开始增加。1995年，板栗瘿蜂的寄生率仅为28%。1994年和1995年，为了确定熊本市板栗螟种群增长滞后的原因，笔者在茨城县的3个板栗果园进行了调查，在这些果园中寄主木栗螟已被寄生蜂控制在低密度。与熊本地区的结果比较发现，不同地区的寄生蜂在成熟幼虫期的死亡率和兼性寄生蜂对寄生蜂的超寄生率存在显著差异；即熊本的死亡率和高寄生率均显著高于茨城市。检测到侵染中华绒螯蟹幼虫的兼性高寄生性寄生虫有：香叶圆尾蛾、褐纹圆尾蛾、细纹圆尾蛾、细纹圆尾蛾和细纹圆尾蛾，其中熊本地区以细纹圆尾蛾和细纹圆尾蛾为主。从初夏到秋季，中华绒球绦虫的成熟幼虫和其亲缘关系较近的本土寄生蜂有益绒球绦虫的滞育期较长。为了确定滞育破茧的条件，在野外采集了中华绒螯蟹的滞育成熟幼虫，进行了初步试验。结果表明，在10 - 15℃的低温条件下，幼虫的滞育行为都可以被打破。即使在10℃的温度下，破滞育后的幼虫仍能发育成成虫。因此，实验应控制在5、10和15 C的条件下，持续5、10和15天来确定破裂条件，并在20或25 C下进行发育。

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.