Genus Stegomyia
The members of this group of mosquitoes, belonging to the sub-family Culicinœ, present very distinctive characters. Their ova, instead of being cemented together to form rafts as in other Culicinœ, are deposited separately, each being surrounded by small air-chambers. Their larvæ are somewhat elongate, with rudimentary antennæ, and a short stout siphon; they maintain art almost vertical attitude. In the nymphæ the trumpets are expanded and broadly triangular in shape. The imago exhibits a distinctive scale structure and, at all events in early life, observes diurnal habits.
The Stegomyiœ are easily recognized by the broad, flat, imbricated scales which completely cover the head and abdomen and which are invariably present on the middle lobe and frequently also on the lateral lobes of the scutellum. These scales give to the insect a satin-like appearance which is quite characteristic. They are mostly small, black insects, with white, silvery, or yellow lines, bands, or spots on the thorax and legs. In India they are known as "tiger mosquitoes" on account of their striped appearance. They seem to have a decided preference for the littoral, and certain species (S. calopus, S. scutellaris) are frequently found on ships and are doubtless distributed by this means. At present the genus Stegomyiœ includes nineteen species, all of which are easily identifiable on account of their striking thoracic and other ornamentation. Of these the type species, S. calopus, is the most important on account of its wide distribution in all tropical and sub-tropical countries, and of its share in the propagation of yellow fever.
S. calopus (Plate VII.) can be recognized by the peculiar lyre-shaped ornamentation of its thorax, composed of two dull yellow parallel lines in the middle and a curved silvery line on each side.*[1] The proboscis is not banded; the abdomen is banded basally; the last hind tarsal joints are all white, and some of the other tarsal joints are marked by light bands basally. This widely distributed species is essentially a domestic form and bites with avidity. It breeds in small artificial collections of water, such as barrels, puddles, cisterns, and even in such small receptacles as sardine tins. The nature of the water appears to be a matter of indifference. The eggs resist a considerable degree of desiccation, and, as they may sink to the bottom of the water in which they lie, are readily pumped into the water-tanks of ships.
Although widely distributed, S. calopus does not occur abundantly in certain parts, such as the Malay States, China, and Africa, where its place is taken by closely allied species, such as S. scutellaris in the Malay States, China, etc., and S. africana, S. argenta punctata, and others in Africa. It is quite possible that, besides S. calopus, other species belonging to the genus may be able to transmit the yellow-fever germ.
- ↑ * This ornamentation is constant, but the median thoracic stripes are absent in a variety called S.fasciata mosquito.
