Ultrastructure of the Spermatophore of a Mealworm Beetle

Abstract

The male mealworm beetle, Tenebrio molitor, transfers sperm to the female by means of a spermatophore, or sperm sac. This study was undertaken to determine the ultrastructure of the spermatophore and the origins of its components.For ultrastructural studies spermatophores were fixed in 3% glutaraldehyde in 0.1 M phosphate buffer, pH 7.2, post-fixed in OsO4,, dehydrated in ethanol and embedded in Spurrs resin. Silver sections were cut on a Reichert Om U2 microtome, stained with uranyl acetate and lead citrate, and examined in a Philips 201 microscope at 60kV.The spermatophore is an elongate sac composed of an inner cylinder within an outer wall. A lumen is located between the outer wall and cylinder, and contains sperm and secretory products from the TAGs (a pair of tubularshaped reproductive accessory glands). The outer wall consists of 4 or 5 concentric layers formed by the secretory products from the paired beanshaped accessory glands (BAGs). The cylinder contains the same layers as the outer wall, but in a reversed order of location, plus a central core which is a mixture of different products and possibly cell debris (Fig. 1).