Comparative morphology and ultrastructure of the corpora allata in newly emerged and sexually mature female Xyleborus ferrugineus (fabr.) (Coleoptera : Scolytidae)

Abstract

The corpora allata (CA) of newly transformed versus sexually matured ovipositing female Xyleborus ferrugineus beetles were compared using both scanning and transmission electron microscopy. The objective was to identify CA characteristics that are unique to each age insect. The surfaces of the spherical CA of newly emerged sexually immature females are initially rough in comparison with the smooth-surfaced CA of the 9-day-old ovipositing adult female. CA are enveloped by a continuous noncellular sheath of varying thickness. Gland cells in CA are closely packed. Some nucleoli of gland cells in CA of ovipositing beetles have a central core which is less electron-dense, but such a core is lacking in the CA of newly transformed females. Mitochondria, with well-developed cristae bathed in an electron-dense matrix, are well dispersed throughout the cells at both stages. Free ribosomes and lysosomes are present in the cells. Golgi complexes are not conspicuous. There is a sparse system of rough-surfaced endoplasmic reticulum (RER). A smooth-surfaced endoplasmic reticulum system is strikingly widespread in the CA cytoplasm of ovipositing females, but is absent in that of the newly emerged females. Neurosecretory axons, filled with electron-dense neurosecretory granules, not only are distributed in the peripheral portion of the CA, but some also penetrate deeply inside the gland. Axons without neurosecretory granules also are present.