Head Adult Mosquito

Mosquitoes, both males and females, can be distinguished from all other Diptera by their long, slender, scaled proboscis. A few other flies also have an elongate proboscis, but it is not covered with scales.

Males of most mosquitoes can be distinguished from females by their verticillate (bushy, not plumose) antennae (sing. antenna). The sections, flagellomeres, of the third antennal segment, the flagellum, bear whorls of setae in both sexes, but in females these setae are relatively short. In the males of most species (not all), the setae on all but the last flagellomere are several times longer and more numerous than in the females.

The head is globular and largely comprised of a pair of prominent compound eyes. The eyes may be touching or separated both dorsally and ventrally. The dorsal surface of the head behind the compound eyes consists of the indistinguishable vertex (anteriorly) and occiput (posteriorly), and is more or less covered by erect and/or decumbent scales. The erect scales are usually truncate or forked apically and often differ in colour from the decumbent scales. They may be numerous, occurring on the vertex and the occiput, or they may be restricted to the occiput, usually in a transverse row. The decumbent scales may be narrow and curved or broad and flat. A row of anteriorly directed, ocular setae arise along the margin of each eye. One or more pairs of interocular setae located at the junction of the eyes (interocular space) are usually longer and project more strongly cephalad than the other ocular setae. The narrow anterior part of the vertex between the eyes bears the frontal tuft characteristic of most Anopheles species. The tuft composed of long setiform scales curving forwards over the frons and clypeus, together with setae and slender but shorter scales.

The antennae, maxillary palpi (sing. maxillary palpus) and the proboscis arise from a frontal area more or less transcribed by the compound eyes. Each antenna is divided into three segments. The basal segment, the scape, is hidden behind the greatly enlarged second segment, the pedicel. The pedicel often bears a group of minute setae or a small patch of scales on its mesal surface. The third segment, the flagellum, is divided into 13 or 14 false segments called flagellomeres. The first flagellomere usually also bears a mesal patch of scales. The remaining flagellomeres are usually without scales. In females, the flagellomeres are about equal in size, but in males of most species the apical two flagellomeres are longer. In genera of tribe Sabethini (e.g. Wyeomyia and Sabethes) and certain other genera (e.g. Hodgesia) the antennae of males resemble those of the females in not having whorls of long setae.

The maxillary palpi are composed primitively of five false segments or sections called palpomeres. In both sexes of anophelines, and in the males of nearly all other genera, the palpus is elongate and all five palpomeres are distinct. A small lobe (palpifer) at the base of the maxillary palpus gives the palpus of males a six-segmented appearance. Because of reduction of the apical palpomeres, the palpus of females appears to be composed of two or three palpomeres. The basal half of the first palpomere in both sexes lacks scales and setae. The rest of the palpus is covered with scales, and the three distal palpomeres (3-5) of males usually have setae.

The proboscis is covered with appressed scales and terminates in a pair of lobe-like labella (sing. labellum). The visible part of the proboscis is largely composed of the labium, which encircles the piercing stylets of the mouthparts. The proboscis is usually more or less straight or slightly curved, but in Toxorhynchites it is bent strongly backwards (reflexed). The labium is closed dorsally by the labrum. The distal part of the proboscis is distinctly swollen in some mosquitoes (e.g. Malaya and males of Ficalbia and Mimomyia).