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General Morphology

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Genera and Species Identification

Genera and species identification can be performed by standard entomological aspects such as exterior, arrangement of eggs, habitus etc. Further and newer techniques include biochemical techniques such as enzyme electrophoresis and gas chromatography of cuticular carbons, and DNA probes. Those have been successfully used to distinguish between morphologically similar species in a species complex (e.g. Anopheles gambiae-complex, Culex pipiens-complex).

Anophelines

Eggs are black, laid on the water surface and possess lateral floats. They cannot withstand desiccation and hatch within 2-3 days, although hatching can take up to 2-3 weeks in colder climates.

The larvae lack a siphon and lay parallel to the water surface where they breathe and feed. They only descend, when they are disturbed.

Larval habitats range from small water aggregations (hoofprints, puddles) to rice-fields and marshy areas, including salt-water marshes and mangrove swamps. Very few species breed in water-filled tree holes and some in leaf axils (of bromeliad plants). Generally clean water without animal or vegetable matter is preferred.

The maxillary palps of adults are long in both sexes, and clubbed in the male (instead of short maxillary palps in females of culicines). Adult Anopheles wings are usually spotted, due to groups of differently coloured scales on the wings. In a resting position adults of this genus have the body and proboscis in a straight line and at an angle to the surface on which they rest. Some species almost seem to "stand on their head". Adults mainly feed in the evenings and at night.

 

Culicines

Eggs of Aedes and Ochlerotatus species are black and usually deposited on damp substrate just beyond the water water-line. They can withstand desiccation, and dry eggs may remain viable for months or even a few years. They hatch when becoming flooded.

Eggs of Culex and Coquillettidia are brownish and laid upright and together, thus forming egg rafts that float on the water surface.

Eggs of Mansonia are laid in a sticky mass that is glued to the undersides of floating vegetation.

Culicine larvae have a short or long siphon, usually used for breathing at the water surface. The larvae of this subfamily hang down from the water surface. Larvae of the species Mansonia and Coquillettidia insert their modified siphon into aquatic plants to obtain oxygen via plant tissues. Pupae also obtain oxygen from plants by inserting into them their specialised respiratory trumpets. Larvae and pupae of these two genera remain submerged.

Some larvae feed near the water surface while others feed on the debris at the bottom of the larval habitat.

Culex larvae have several pairs of hair tufts on their breathing tube, which is relatively long and slender, whereas Aedes larvae have a short and stout breathing tube with only a single pair of hair tufts.

 

Larval habitats

They show a wide variety. Especially Aedes and Ochlerotatus breed in natural and man-made container-type habitats (tree holes, cut bamboo stems, discarded cans and tyres, etc.). Culex larvae are mainly found in ground collections of water (pools, ponds, ditches, borrow pits). Some breed in rice-fields, while others tolerate high levels of organic pollution, using latrines, septic tanks and soak-away pits. Mansonia and Coquillettidia larvae and pupae are only found in waters with aquatic plants to attach themselves.

 

Adults

Adults of many Aedes and Ochlerotatus species bite during the day or early evening, while adults of many Culex and most Mansonia and Coquillettidia species bite at night. Most culicines feed and rest outdoors. The wings of these genera are not spotted.

Adults of the culicines have their body in a resting position more or less parallel to the surface with the proboscis bent down. Detailed differentiation of the single culicine genera can be aided by the appearance of bristles (see Borror and DeLong, 1971).

Two types of feeding have been described by Gordon and Lumsden (1939): 'pool feeding', in which a capillary is ruptured by the tip of the fascicle and the blood is sucked from the small pool formed by the ensuing haemorrhage; and 'capillary feeding', in which the blood is taken up as a result of the fascicle penetrating into the lumen of a capillary.
In general mosquitoes are capillary, some are pool feeders (Mehlhorn, 2001).

   

Further information

  • Borror DJ, DeLong DW: Order Diptera. Suborder Nematocera. In: Borror DJ, DeLong DW (eds.): An introduction to the study of insects. 3rd edn., 1971, Holt, Rinehart & Winston Inc., New York, pp 492-504
  • Gordon RM, Lumsden WHR: A study of the behaviour of the mouthparts of mosquitoes when taking up blood from living tissue; together with some observations on the ingestion of microfilariae. Ann Trop Med Parasitol. 1939, 33, 259-78
  • Mehlhorn H: Mosquitoes. In: Mehlhorn H (ed.): Encyclopedic reference of parasitology. Biology, structure, function. 2nd edn., 2001, Springer Verlag, Berlin, pp. 378-84

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