DNA synthesis by testicular follicles in a lady-beetle, Coccinella septempunctata brucki (Coleoptera: Coccinellidae) in relation to aestivation diapause

Abstract

Summary The present study confirmed that imaginal aestivation diapause in the seven-spotted lady-beetle, Coccinella septempunctata brucki, was characterized by the arrested reproduction not only in females (Okuda and Chinzei, 1988) but also in males. Changes in spermatogenesis by the testicular follicles and development of the male accessory gland were observed during prediapause, diapause and the post-diapause period. DNA synthesis by testicular follicles was examined as a criterion to assess spermatogenesis. DNA synthesis in the testicular follicles from pre-diapause male adults was as active as that from post-diapause ones. DNA synthesis gradually decreased with the induction of diapause and reached minimum activity on day 30 after emergence. Later DNA synthesis gradually resumed and reached its maximum activity when the male adults completed diapause on day 120. The male accessory glands developed intermediately during the pre-diapause period based on total protein content, which showed its minimum value in the middle of diapause and regeneration occurred with the termination of diapause. Methoprene treatment to diapausing male adults induced reproductive activation, i.e., increases of DNA synthesis by the testicular follicles and protein content of the male accessory glands. In contrast to the in vivo results, 5-h incubation of testicular follicles from diapausing males in Grace's medium containing methoprene induced no significant elevation of DNA synthesis. Histological study suggested an occurrence of a diapause-specific lipid in the testicular follicles, and this was confirmed by thin layer chromatography analysis.