DEVELOPMENTAL MORPHOLOGY OF STEM GALLS OF DIPLOLEPIS-NODULOSA (HYMENOPTERA, CYNIPIDAE) AND THOSE MODIFIED BY THE INQUILINE PERICLISTUS-PIRATA (HYMENOPTERA, CYNIPIDAE) ON ROSA-BLANDA (ROSACEAE)

Diplolepis nodulosa (Beutenmuller) induces small, single-chambered, pr osoplasmic galls in stems of Rosa blanda Ait. Gall initiation begins w hen adult females deposit a single egg into the procambium of R. bland a buds. Pith cells at the distal pole of the egg lyse forming a chambe r into which the hatching larva enters. Cells lining the chamber diffe rentiate into nutritive cells, which serve as the larval food. Gall gr owth is characterized by the proliferation of parenchymatous nutritive cells causing gall enlargement. A separate gall vasculature does not form, but instead, gall tissues are irrigated by the existing stem vas culature. Maturation begins when gall tissues cease proliferating and differentiate into distinct layers concentrically arranged around the larval chamber. The innermost layer is composed of cytoplasmically den se nutritive tissue, followed by parenchymatous nutritive tissue, scle renchyma, cortex, and epidermis. Parenchymatous nutritive tissue diffe rentiates into nutritive tissue and is consumed by the larva. Galls of D. nodulosa are susceptible to anatomical modification by the phytoph agous inquiline Periclistus pirata (Osten Sacken). Galls attacked by P . pirata become enlarged and multichambered, with little resemblance t o inducer-inhabited galls. Periclistus pirata kill the larva of D. nod ulosa at oviposition and deposit several eggs per host gall. Inquiline -occupied galls may contain the eggs of several females. Nutritive tis sue induced by D. nodulosa disintegrates. Growth of attacked galls occ urs prior to hatching of P. pirata eggs. At egg hatch, the gall appear s as an enlarged hollow sphere and larvae disperse over the chamber su rface and feed on parenchymatous tissue. Feeding induces tissue prolif eration, which surrounds each larva within its own chamber. As galls m ature, cells surrounding each larval chamber lignify forming a scleren chyma sheath. Cells inside the sclerenchyma sheath differentiate into nutritive cells and are consumed by the inquiline larvae.