Validity of the “Greenish Gall” as an Indicator for Evaluating the Effectiveness of Parasitoids (Hymenoptera : Chalcidoidea) of Dryocosmus kuriphilus Yasumatsu (Hymenoptera : Cynipidae)

Abstract

It was suggested that the chestnut galls inhabited by parasitoids would remain greenish in color until autumn (Yasumatsu, 1955). An evaluation of the effectiveness of an introduced Torymus (Syntomaspis) sp. had been made by the abundance of such greenish galls (Torii, 1959). In order to clarify whether it is reliable to apply this method for field experiments, greenish and brown galls were collected to examine in autumn from Mt. Aburayama, Fukuoka. The results are as follows: (1) Although the ratio of galls inhabited by live parasitoids is higher in greenish galls than in brown ones, greenish galls are not always parasitized and brown galls are frequently inhabited by parasitoids. (2) Gall color is not determined by any inhabiting species of parasitoid. (3) Greenish galls tend to be smaller in size and contain fewer emergence holes. (4) Galls withered rapidly after cynipid or parasitoid wasps had emerged because they injured the gall tissue on emergence. (5) Evaluation of the effectiveness of Torytnus (S.) sp. by the abundance of green ish galls in autumn is not a reliable indicator of the actual parasitoid incidence. Dissection of galls remains the only reliable method of accurate estimates of para sitoid abundance.