Fine structure of the reproductive system of Chrysomya megacephala (Diptera: Calliphoridae): the external sexual organ.

The fine structure of the reproductive system of Chrysomya megacephala (Fabricius), a blow fly species of medical importance, was studied using scanning electron microscopy (SEM) to contribute detailed morphological information on the external sexual organs or genitalia of this species. Analysis of the male genitalia or hypopygium revealed that the epandrium is a broad organ resembling a crescent shape, while the ejaculatory apodeme and aedeagal apodeme show similarity in their lengths. The cercus is significantly longer than the surstylus with its apical end being more or less rounded. Dense patches of long bristles, morphologically similar to the sensilla chaetica and sensilla trichodea, were found along the lower half of the cercus. The surstylus has a stout triangular shape, and the proximal half is greatly endowed with sensilla thought to be sensilla chaetica and sensilla trichodea. The aedeagus per se is prominent and has a clavate shape formed by the base theca and elongated phallus. The vesica of the phallus is a smooth bilobed structure, which curves inward. The juxta and juxta process are armed with many rows of strong spines resembling thorns in their appearance. The harpe is slender, recurved anteriorly, and distally pointed like a sickle. Regarding the female genitalia or ovipositor, SEM observation of the supraanal plate revealed it to be sclerotized and more or less triangular-shaped, lying between a pair of short cerci. Several types of sensilla were found on the supraanal plate, subanal plate and cercus, including the sensilla trichodea, sensilla basiconica, sensilla placodea, and probably, sensilla styloconica. The possible functions of sensilla distributed in particular regions of the fly genitalia are discussed.