Mortality Factors of the Chestnut Gall-wasp, Dryocosmus kuriphilus Yasumatsu (Hymenoptera : Cynipidae) after Gall Formation

概要

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In chestnut galls formed by Dryocosmus kuriphilus, empty chambers with no emergence traces of either D. kuriphilus or parasitoids (type-N chambers) are frequently observed. A classification was made of the contents of chambers for galls collected from 13 wild chestnut trees in late November, 1988, in mid March, from mid May to late July and in late November, 1989, in order to examine the factors involved in the formation of these type-N chambers. The mean monthly proportion of type-N chambers in comparison with all types of chamber was significantly different amongst the trees between May and July. The proportions of both type-N chambers and parasitism on D. kuriphilus by parasitoids varied greatly amongst the trees, ranging from 0.4% to 40.7% and from 24.5% to 75.8%, respectively, but did not differ significantly between the sampling dates after mid June in most trees. The mean proportion of type-N chambers after mid June in each tree was positively correlated only with the mean proportion of parasitism by Torymus beneficus hibernating at the pupal stage. These data suggest that the formation of type-N chambers in this study area was due not to plant resistance, but to host feeding by T. beneficus hibernating as pupae. This also implies that addition of the type-N chamber to direct parasitism should be made in evaluation of the overall mortality of D. kuriphilus.
日本昆虫学会の論文
1999-12-25