Mosquito Taxonomic Inventory

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Abbreviation:

G

Variants:

Pl. genitalia (no singular form)

Definition:

In general, the abdominal structures involved in reproduction. In the narrow or strict sense, the external structures of abdominal segment IX. In mosquitoes, applied to abdominal segments IX (the genital segment) and X (parts of the proctiger may take part in the copulatory process); in some species, abdominal segment VIII may be sexually differentiated from the preceding ones in one or more details and would in such cases be treated as a part of the genitalia.

Explanation:

(1) The term genitalia is used in place of “terminalia” because there are other terminal points on the insect body and also because it is difficult to state definitely which of the terminal structures do not somewhere in Culicidae play a role in copulation.

(2) The 180º rotation of the complex of anal and genital parts occurring caudad of abdominal segment VII in male mosquitoes a few hours after emergence has created much confusion in the morphological and taxonomic literature. In an effort to solve this, the terms “tergal” and “sternal” have sometimes been used. This usage is equally confusing because many parts of the genitalia are neither tergal nor sternal in origin. Consequently, the terms “dorsal” and “ventral” are used herein in the prerotation sense, i.e. with their true morphological connotation.

(3) One of the oldest concepts and one that has gained wide acceptance at various times since its inception is that insect genitalia (specifically abdominal segment IX, sensu stricto) have been derived from segmental appendages. The appendicular theory of origin for insect genitalia has been supported by a long list of workers (Smith, 1969). As originally developed, it held that the genital appendages were derived from the endopodites or exopodites of the coxopodites and/or telopodites and thus were serially homologous with the limbs of other segments.

Snodgrass (1957) showed that the external male genitalia of the Thysanura and Pterygota arise from paired rudiments, primary phallic lobes, usually located behind abdominal sternum IX. Except in certain Orthoptera where the genitalia develop from embryonic appendages, the rudiments always appear during postembryonic development. For this reason and because the undifferentiated rudiments give rise to very different structures in different groups (see Matsuda, 1976), some workers denied the appendicular origin of the genitalia, e.g. Matsuda (1958) and Snodgrass (1963). But as Matsuda (1976) notably disclosed, the appendicular theory is applicable and homologies can be traced if the developmental principles of heterochrony and substitution are applied to the study of the genitalia.

Matsuda's concept of appendicular origin of insect genitalia is followed here, a position which, when applied to the Culicidae, required the replacement of several commonly used terms. It should be noted that Matsuda has discredited Smith's (1969) conclusion that the genitalia in both sexes are homologous, structure for structure, in all insect orders.

(4) Ontogenetic studies (Christophers, 1922; Anderson, 1967; Horsfall & Ronquillo, 1970) have shown that the male genitalia (sensu stricto) of mosquitoes arise from paired imaginal discs (genital plaque of Christophers, 1922; imaginal disc 9 of Horsfall & Ronquillo, 1970) located in the anterior part of abdominal segment X of the larva (the posterior part of embryonic abdominal segment IX). The discs become buds that later evert and develop into the primary phallic lobes (proandropodite of Christophers, 1922; bilateral bud of Horsfall & Ronquillo, 1970). As growth proceeds, a mass of tissue on the posterior surface of each lobe forms the “hypandropodite” of Christophers (1922) and the remaining tissue becomes the gonocoxopodite. The hypandropodite usually proliferates at the basomesal margin of the gonocoxopodite, but in certain taxa a portion of it becomes part of the phallosome (the leaflets of aedeagus in Anopheles and the ventral arms in Culex). Freeborn (1924) dubbed the combined hypandropodites exclusive of the phallosomal structures the “interbasal fold” (harpaginal fold of Christophers, 1922; harpagonal fold of Christophers, 1960) and described the variously developed hypandropodital parts as projections of this. The structures formed from the hypandropodite at the base of the gonocoxopodite include the claspette, basal mesal lobe, parabasal lobe and subapical lobe. The homologies or partial homologies of these are uncertain.

Synonyms:

For male: genitalium, hypopygium, terrninalia, terminalium, copulatory apparatus; for female: hypopygium, ovipositor, terminalia.