In vitro survival and amethopterin effects on the structure of ovarian tissues of the sawfly, Acantholyda nemoralis Thoms.

Whole ovaries of the sawfly, Acantholyda nemoralis Thoms., Tenthredinidae, Hymenoptera, were cultivated by the organ culture technique of Fell in the medium of Jones and Cunningham modified by doubling the contents of salts, sugars and lactalbumin hydrolysate and supplemented with an addition of folate. In the experimental conditions the sawfly ovary survived for several days showing mitoses in the follicular epithelium. In some of the nurse cell nuclei of the cultured ovaries nucleolus-like structures developed which showed a positive reaction to the Hamm test for viral polyhedra. Formation of these structures was stimulated by amethopterin. Electron microscopical examination revealed that these structures were not viral polyhedra but enlarged nucleoli whose modified ultrastructure differed considerably from that of the nucleoli of cells of trophic ovaries in normally developing insects. Amethopterin appears to induce enlargement of the granules of the granular component of nucleolonema, probably due to disturbance in RNA biosynthesis. The positive Hamm test obtained in the nucleoli shows that this test cannot be regarded as specific for nuclear polyhedra.