The structure and evacuation of the spermatophore of Tenebrio molitor L. (Coleoptera: Tenebrionidae)

Sperm are transferred from male to female mealworm beetles within a spermatophore. The highly organized spermatophore can be visualized as a tube, blind at both ends, and invaginated at the anterior. The wall of the tube is composed of two layers, one of fibrous protein and the other of lipoprotein which appears frothy in electron micrographs. After being deposited in the bursa of the female, or placed in saline, the spermatophore undergoes sequential stereotyped expansions at the anterior tip and then bursts, releasing semen within the female bursa. The ‘evacuated’ spermatophore becomes coated by a transluscent layer and is ejected from the female 18 hr after copulation.