Comparison of the development of stem galls induced byAulacidea hieracii(Hymenoptera: Cynipidae) on hawkweed and byDiplolepis spinosa(Hymenoptera: Cynipidae) on rose

Abstract

Plant galls induced by two distantly related species of cynipid wasps, Aulacidea hieracii Bouché, which belongs to a basal lineage and induces galls on Hieracium umbellatum L., and Diplolepis spinosa (Ashmead), which belongs to a derived group and induces galls on Rosa blanda Ait. and Rosa rugosa Thunb., were compared. As gall characters are determined by the wasp rather than the host plant, we hypothesized that information on gall development would contribute to our understanding of the evolution of the cynipid complex. Galls induced by both species are spherical and multichambered and arise on stems. All stages of gall development were examined including host plant response to oviposition and the eggs, gall induction, reaction of the plant to larval feeding, and the formation of nutritive cells, vascular tissues, and sclerenchyma within the gall during growth and maturation. Galls of A. hieracii develop in a manner similar to galls inhabited by inquiline cynipids, a basal lineage to which they are closely related. Aulacidea hieracii lay eggs in a sticky cluster, the eggs cause proliferation of nearby stem tissues, and freshly hatched larvae crawl to sites where each induces a separate chamber. Galls of D. spinosa are induced from eggs deposited in slits between the base of leaf primordia near the tips of leaf buds with one end of the egg touching the procambium. Freshly hatched larvae enter a cavity that forms beneath each egg. Galls of A. hieracii exhibit anatomical and developmental features that are less complex and intricate than are the galls of D. spinosa. The term “asterids” is proposed for cynipid galls that are developmentally and anatomically simple and develop on herbaceous plants and the term “rosids” for cynipid galls that are developmentally and anatomically complex and develop on woody plants such as roses and oaks.