Morphological and ultrastructural organization of the male genital apparatus of some Aphididae (Insecta, Homoptera)

Ultrastructural investigations on the amphigonic reproductive mechanisms in Aphidoidea (Homoptera, Sternorryncha) species, of which little is known in the literature, can provide useful information on their reproductive biology. Morphological and ultrastructural investigations were carried out on the reproductive tract and on spermatozoa from sexually mature males of five species belonging to three subfamilies of Aphidoidea. The organization of the reproductive tract and of spermatozoa appears simple and similar in the examined species. Each testis consists of three follicles containing many cysts arranged in a progressive order of maturation from the distal to the proximal tract; spermiogenesis only occurs in sexually mature males, ending with the organization of sperm bundles. Gametes are neatly arranged in each bundle and kept together by a cap showing a particular organization. The distal tract of each spermiduct is enlarged and full of gametes; close to the testis the two spermiducts merge together, except in Drepanosiphum platanoidis where the spermiducts run independently. The various tracts of each examined gland showed no peculiar differences either in the same species or among the species. Some interesting hypotheses are proposed in this work about the probable roles of the investigated structures in the reproductive mechanisms of these insects.