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R. B. JACKSON
species, eg. the tiger mosquito with white and black markings on leg and body, can withstand drying for months and larvæ hatch out, but usually eggs will not endure dessication for any length of time. The egg varies from I to 12 mm. long or 2/50 to 3/50 inches. Inside the egg a larva develops
and after a few days emerges to live in the water.
CULICINE LARVA
MOUTH BRUSHES
ANOPHELINE LARVA
ANTENNAE
MOUTH BRUSHES
ANTENNAE
EYES
PEYES
TRACHEA
ALIMENTARY
CANAL
TRACHEAL GILLS
SIPHON
Diagram of Larvae.
-SPIRACLES
TRACHEAL GILLS
The larva has a head, thorax, and abdomen, the head has a pair of antennæ resembling horns, a pair of eyes, a mouth, and a pair of mouth brushes. These brushes are situated one on each side of the mouth and can sweep particles into it.
Some larvæ are cannibal in their habits and will even prey on their own kind. Such cannibal larvæ, however good their appetites, are not a solution to the problem of mosquito destruction, as they are usually only found flourishing in special places, or else are in a great minority to their potential victims. The mouth leads into a tube known as the alimentary canal which passes through the thorax and abdomen opening at the end of the abdomen and is surrounded by two pairs of structures called gills.
The abdomen consists of nine segments.
The larval breathing system consists of trachea, or tubes resembling wind pipes, there are two main
The Hong Kong Naturalist.
A Brief Account of Mosquitoes
209
trachea each extending into head, thorax and abdomen and dividing into smaller branches.
Mosquito larvæ may be divided into Culicine and Anopheline. In the Culicine larvæ the trachea are continued as a breathing tube (known as a siphon) through the 8th abdominal segment; in the Anopheline larvæ the trachea are not prolonged into a siphon but open by two orifices called spiracles on the 8th segment. A Culicine larva rests at an angle to the surface of the water head down and siphon uppermost, this position enables it to take in air; the Anopheline larva remains parallel to the surface of the water as it obtains air through its spiracles. But in Hong Kong some Culicine larvæ rest more or less parallel to the surface of the woter: one of the mosquitoes called after Dr. Macfarlane, formerly Government Bacterio- logist, namely Uranotenia macfarlanei rests thus, but the presence of a siphon will prevent its being mistaken for an Anopheline larva. In another kind of Culicine larva the siphon is specially modified as the larva is attached to the roots of certain plants from which it obtains its oxygen without coming to the surface of the water.
The modification consists in the presence of tiny hooks at the end of the siphon for attachment to the plant and the notching of an edge of the siphon.
This variety occurs in the Island, the mosquito which results is a ferocious biter and unless the mosquito can be recognised so that the peculiar habits of its larvæ are understood; attempts to deal with its breed- ing places are not likely to be successful as oiling is of no avail.
Mosquito larvæ grow and throw off skins three times during the course of their development, these cast-off skins, if preserved and mounted, will usually show as many details as the larvæ from which they are derived. In a collection of larvæ from the same place various different species may be found. To make sure what mosquito a given type of larva will correspond to, it is necessary to put the larva in a little water in a test tube by itself; cover the mouth of the test tube with muslin. Make a permanent prepara- tion of such skins as it throws off in the process of development, and preserve the mosquito which emerges, From the larva a comma-shaped body results which is very active but does not feed. This is called a pupa. After a few days the skin of the pupa splits and a mosquito emerges, the mosquito remains standing on the pupal case until its wings have dried, it then flies away. The mosquito larva is best studied under a microscope.
The
The mosquito consists of head, thorax or chest, and abdomen. head has two pairs of kidney-shaped eyes; from between the eyes project a pair of slender jointed rods known as antenna, the joints carry whorls of hairs, in the female the whorls are sparse and wispy but in the male they are thickset or bushy so as to present a bottle brush appearance. Standing out from the head â long rod-like structure called the proboscis which consists of a sheath containing the biting and suctorial parts. These form a double tube, when in action the blood, and any malarial or other parasites in it, goes up one tube to reach the mosquito's midgut or stomach: down the other tube the mosquito's salivary secretion flows which enters the wound and if the mosquito is an Anopheline with malarial infection in its salivary glands, this infection finds its way into the body. Male mosquitoes do not
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