Maxillae and Mandibles of Male Mosquitoes and Female Autogenous Mosquitoes (Diptera: Culicidae)

Abstract

Maxillae and mandibles of males of 44 species of 12 mosquito genera and females of three autogenous genera and two partially autogenous species were examined under light microscopy and scanning electron microscopy. The maxillae and mandibles of male mosquitoes are delicate, tape-like structures with lengths characterizing genera or higher level classification units. Five patterns are recognized: (A) long maxillae and mandibles with mandibles longer than maxillae in Anopheles; (B) long maxillae and mandibles with maxillae longer than mandibles in Toxorhynchites; (C) short or intermediate lengths of maxillae with short mandibles in Aedes, Armigeres, Culex, Ochlerotatus, Orthopodomyia, and Uranotaenia; (D) short or intermediate length of maxillae with no mandibles in Mimomyia and Tripteroides; and (E) no maxillae and mandibles in Malaya and Topomyia. Maxillary and mandibular lengths of male mosquitoes show a positive correlation. Length of maxillae and mandibles of autogenous females are reduced to the same level as conspecific males. In contrast, females of partially autogenous species have complete maxillae and mandibles as in females of anautogenous species.

The Hypopharynx of Male and Female Mosquitoes

“…Differing from male mandibles and maxillae that probably have no function, the salivary canal of males functions as a closed tube by its dorsal overlapping edges, as in females [1,2,8]. Saliva secreted by salivary glands of males containsglucosidase, -amylase and bacteriolytic factors, but lack the polypeptide D7, sialokinins I and II, and apyrase which are secreted from the median lobe and the distal portion of lateral lobes of female's salivary glands [2].…”

“…pipiens molestus and Oc. togoi showing that even though these mosquitoes do not use their hypopharynx as blood feeding females did, they still retain the clue of their common ancestor's attributes on hypopharynx and other mouthparts such as maxillas and mandibles in some degrees [1,20], so, the fused hypoharynx of Malaya should derived from an older attribute of their origin; (2) geographic distribution of genus Malaya confined only for Southeast Asia and Papua regions [25,29], showing that this genus might evolved recently in mosquito evolution and hence derived their fused hypopharynx from an older mosquitoes that had a free hypopharynx as other mosquitoes did; (3) phylogeny analyses by Harbach and Kitching, using morphological characters-based cladograms, placed this genus as the most recent group appeared in mosquito evolution [32]. The hypothesis suggests that the genus represents the most advance stage in evolutionary process of the hypopharynx, and that such evolution occurred independently from other autogeneous genera.…”

“…It is also possible that the hypopharynx fused with the labium is found in life-time autogenous species yet to be examined. We revealed the diverse states of male maxillae and mandibles [1,6], and noted that expansion of the scope to all the mosquito tribes and genera could contribute to phylogenic study of mosquitoes. Though the hypopharynx with functions is much less variable, it could still yield cues to understand the evolution of feeding habits of mosquitoes.…”

“…Materials used were the same with those used for examination maxillae and mandibles of male mosquitoes in our previous study [1] listed in Table 1. The hypopharynx states of males of 44 species of 12 genera, females of 2 partially autogenous and 5 autogenous species were examined.…”

“…During blood feeding, the fascicle (contains a labrum, a hypopharynx, pairs of mandibles and maxillae) enters the host skin, while the labium-formed sheath remains outside the skin. The maxilla and the mandible function as piercing organs [1,2], but there is no active movement of the hypopharynx. No muscles are either originated from or inserted on the hypopharynx [2].…”