This section is from the book "Malaria, Influenza And Dengue", by Julius Mennaberg and O. Leichtenstern. Also available from Amazon: Malaria, influenza and dengue.
The perfect insect does not feed for some time (twenty four hours) after hatching. When first hatched, their wings are soft and they fly but feebly when disturbed. The hatching may be studied by collecting a number of pupae and placing them in a tumbler. The male is easily distinguished from the female by the long, plumose antennae. The palpi are also long and hairy in the male, and in some genera expanded terminally, giving the end of the proboscis a characteristic appearance, often of practical use when capturing mosquitos in ill lighted outhouses, native huts, etc. The commonest mosquitos belong to the subfamilies Anophelince, Culicince, and Aedeomyince. The Anophelince, which concern us mainly, as they take part in the transmission of malaria , are, without the use of scientific characteristics, readily recognized by the layman.
(1) In the Anophelince the palpi are as long as the proboscis in the females; in the Cidicince they are quite short in the females. In the Aedeomyince they are short in male and female.
(2) The Anophelince can almost at a glance be recognized by their attitude, which is characteristic, though variations occur in the different genera. In the Anophelince the angle which the proboscis makes with the body is a slight one, 15° in P. stephensi, while in the Culicince, e. g., in the genus Tceniorhynchus, it is 45°. The result of this is that the Anophelince have a characteristic, awl like aspect, while the Culicince, etc., are humpbacked. Two only of the Anophelince so far described have this aspect of the Culicince, viz., M. culicifacies, and [A] culiciformis, both Indian species.
(3) Hence also the attitude when at rest is different. The body of the Anophelince projects from a wall at an angle varying from 5° to almost 90°, while in other Culicidce the body lies nearly parallel, with the hind end closer to the surface than the thoracic end.
(4) The Anophelince have, as a rule, spotted wings, though there are exceptions to this rule-viz., A. immaculatus and A. aitkeni, both Indian species; A. bifurcatus (Europe), A. algeriensis, A. nigripes (Europe and America), A. stigmaticus (Australia). And, on the other hand, some of the other subfamilies have spotted wings-e. g., in the genus Theobaldia of the subfamily Culicince, Culex mimeticus in the Culicince (in attitude also this mosquito is said to resemble an anoph eline), the genus Lutzia, etc.
Oviposition was described one hundred and fifty years ago by Reaumur. Miall gives the following account of the process: The mosquito rests the four front legs on the margin of a pool or floating object. The hind legs are crossed, and in the angle between them the eggs are laid; as the number increases the legs become more and more parallel. This description will serve for the method adopted by C. pipiens, as described by Taylor. According to Gray, when rafts are being laid and the process is complete, by a movement of the hind legs the raft is tilted so that the eggs stand on end. The egg rafts of the Culicince are well known objects, and are to be found on the surface of uncovered tubs of water, etc., in the tropics. The rafts consist of a mass of eggs arranged vertically, with the pointed end uppermost; the thick end, which contains the head of the larva, lies downward. Little systematic work has so far been done on the eggs of the different genera. We can, however, say occasionally, by examining the rafts, what genus we are dealing with; thus the egg raft of Taeniorhynchus is larger and more slender than that of Culex. The rafts vary in the case of Culex from one third to one fifth of an inch in length, and may contain some hundreds of eggs. Further, according to Taylor, of Havana, considerable differences occur in the size of the rafts and of the individual eggs in various species of the same genus, and, moreover, the eggs of all species of Culex are not laid in rafts, but some are laid singfy, and in the mode of oviposition also differences occur. Taylor gives the following data: Culex pipiens: the rafts contain 200 to 400 eggs; the egg measures 0.9 mm. by 0.16 mm. Culex nigritulus: the rafts contain 200 to 300 eggs. The eggs are 0.6 mm. by 0.14 mm. Uranotcenia lowii: the rafts contain 50 to 75 eggs. Stegomyia fasciata: deposited singly. The average number of eggs is 50. The surface of the egg is described by some authors as finely reticulated and having fine air bubbles attached to it; others describe a rudimentary "float" structure. The eggs of S. notoscripta are laid in rafts. Various species of Culex and Psorophora also lay their eggs singly, e. g., Culex sol licitans, Culex tceniorhynchus, Culex confirmatus, Culex jamaicaensis, Psorophora howardii. Further, the eggs of these two latter have laterally well marked spines. Some species of Psorophora and Muc idus also lay their eggs singly.
It is in the Anophelince, however, that we have the most specialized eggs. The eggs are not easily seen in natural pools, except where, as sometimes occurs in the tropics, the whole surface of a sheet of water is one continuous sheet of ova, larvae, pupae, and escaping full grown insects. They may be, however, collected on the surface of wet mud, or they may easily be procured by capturing gravid females in native or other quarters and confining them under a net and supplying a shallow saucer of water, etc. It can then be observed that the eggs are laid singly, but that when they come in contact on the surface of the water, they arrange themselves side by side or in very regular star patterns. With a microscope the floats and frill can easily be observed and differences in the eggs of the various genera can be studied (p. 181). The Anophelina will deposit their eggs occasionally in a test tube in the absence of water. They will also lay them in little heaped up masses on the surface of moist mud. The eggs are at first colorless, but rapidly darken. The resistance of eggs to desiccation is comparatively slight, or, to speak more accurately, we should confine our remarks to the eggs of the Anophelince. Dried for two or three days on paper in the tropics (temperature, 86°-96° F.), they do not hatch out subsequently (vide also p. 183). The eggs of the Cidicidce, as a whole, appear to be but slightly resistant to desiccation, but those of Stegomyia fasciata are remarkably resistant and will hatch out in water after having been kept dry for as long as three months, and Theobald has also hatched out in England eggs of this species sent him from the tropics. Further, it is stated that eggs laid in October and November (in Europe), which is the latest time for laying, will survive in dry pits and eventually hatch out in the subsequent spring.
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