10.シバヤナギハウラタマフシにおける虫えい形成機構に関する研究(口頭発表)

概要

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Galls are abnormal plant tissues formed by parasitic insects on various plant parts. It is generally assumed that the insect secretes chemicals at oviposition or ingestion, which induce abnormal cell growth and proliferation leading to gall formation. The active substances, however, have yet to be identified. In this study, we selected a willow (Salix japonica) gall formed by a sawfly of the genus Pontania. The detailed observation by Hovanitz (1959) indicated that the gall formation is initiated by the liquid (accessory gland fluid) at oviposition and is further developed by saliva at larval ingestion. Here we examined the possibility that auxin takes part in the gall formation. Although the involvement of auxin in gall formation has long been argued, there was no evidence that the gall-forming insects have ability to synthesize auxin. LC-MS/MS analysis indicated that accessory gland fluid taken from female adult abdomen contained indole-3-acetic acid (IAA) at several times higher concentration than that in normal willow leaves. On the other hand, the level of IAA in larvae was more than 100 times higher than that of the willow leaves. The feeding experiment clearly indicated that the larvae can synthesize IAA from tryptophan. These results suggest that the IAA plays a key role in gall formation.
2010-10-01