The Induction of Gall Formation in Ageratina riparia by Procecidochares alani (Diptera: Tephritidae). I. Gall Histology and Internal Gross Morphology of the Third Instar

摘要

Gall formation in the composite, Ageratina riparia, is induced by the presence and activity of the larval stages of the gall-forming tephritid, Procecidochares alani (Steyskal). The tephritid spends its entire larval stage in the subapical area of the stem and its activity causes the formation of a bulbous shaped gall. Histological examination of the gall reveals an abundance of secretory ducts external and sometimes internal to the vascular cylinder; doubled vascular bundles; "faisceaux d'irrigation"; an increase in phloem and pith parenchyma accompanied by a decrease in xylem; nutritive cells; and an increase in stem diameter due to hyperplasia of the pith area. Morphologically, P. alani third instars possess structures generally characteristic of other cyclorrhaphous dipteran larvae. However, a yellowish membranous structure was found attached to the distal part of the most anterior pair of Malpighian tubules which appears to be unique to gall flies in the genus Procecidochares. This pair of structures, termed "yellow bodies," increases in size with each succeeding instar, decreases in size during pupariation, and is absent 2 to 3 days into the pupal stage. The proposed function of this structure is discussed.