Genus Culex and genus Anopheles: morphological differences. Phlebotomus papatasi

Genus Culex and genus Anopheles: morphological differences. Phlebotomus papatasi

The two-winged flies that carry the most disease. Anopheles carries malaria, and filariae in the countryside; Culex carries filariae in towns and viruses such as West Nile. They are told apart at every stage, from the egg to the resting female. The sand fly Phlebotomus papatasi, a tiny hairy fly that rests with its wings raised, carries Leishmania and the sand fly fever viruses.

Anopheles and Culex compared
Two columns, Anopheles on the left and Culex on the right, and down the page the same stages of each. The eggs on the water, seen from above: Anopheles's lie apart, each a dark boat-shaped egg with a pale ribbed float along either side; Culex's stand on end, stuck together in a dark, boat-shaped raft. The larva in the water, seen from the side: the Anopheles larva lies level just under the surface, its back along it, breathing through a small plate of spiracles on its back near the tail; the Culex larva hangs head down at an angle from the surface by a long breathing tube, the siphon, near its tail. The pupa: in both a comma, a large rounded head and thorax with a curled abdomen, hanging from the surface by two small breathing trumpets. The female at rest on a surface, seen from the side: Anopheles tilts up at an angle, her proboscis, head and body in one straight line, her wings, in most species, spotted with dark scales; Culex holds her body level with the surface and her head bent down, her wings clear. At the bottom, each female's head enlarged: Anopheles's palps are as long as her proboscis, Culex's are short.

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Anopheles carries malaria, and filariae in the countryside; Culex carries filariae in towns and viruses such as West Nile. They are told apart at every stage: the eggs laid one by one with floats, or in a raft; the larva lying level without a siphon, or hanging from one; the female resting tilted with long palps and usually spotted wings, or level with short palps and clear wings.

Simplified: each row drawn to its own scale, the two genera in a row to the same one, except the Culex raft, drawn smaller than the Anopheles eggs beside it; the eggs seen from above, the rest from the side; the bodies drawn simply in one muted colour, without their scales and most of their hairs; the larvae's mouth brushes and tufts of hairs drawn as a few lines, and the larva's head turned for feeding at the surface not shown; only the female's legs on the near side drawn, and the antennae left off the enlarged heads; the two pupae, which look much alike, drawn the same.

3 sources
  1. Centers for Disease Control and Prevention. Life cycle of Anopheles mosquitoes. 14 May 2024.
  2. Centers for Disease Control and Prevention. About Culex mosquitoes.
  3. Wikipedia. Anopheles; Culex; Mosquito.

At a glance

  1. Mosquitoes and sand flies are two-winged flies, Diptera, with complete metamorphosis: egg, larva, pupa and adult. Only the females take blood, which most of them need to make their eggs.
  2. Anopheles carries malaria: it lays its eggs singly, each with two floats; its larva has no siphon and lies level under the surface; the female rests tilted, abdomen up, her palps as long as her proboscis, her wings usually spotted.
  3. Culex carries Wuchereria in towns and viruses such as West Nile and Japanese encephalitis: it lays its eggs in a raft; its larva hangs head down from a siphon; the female rests level, with short palps and clear wings.
  4. Aedes bites by day and carries dengue, yellow fever, Zika and chikungunya; the tiger mosquito, Aedes albopictus, now lives in much of Europe.
  5. Phlebotomus papatasi is a sand fly: tiny and hairy, with large black eyes and long legs, its hairy wings raised over its body at rest, its young stages in damp soil, not water. Sand flies carry Leishmania and the sand fly fever viruses, and can pass through an ordinary mosquito net.

Mosquitoes

Mosquitoes, family Culicidae, are two-winged flies of the order Diptera, in the class Insecta. Three genera matter most in medicine: Anopheles, Culex and Aedes. The diseases they carry kill hundreds of thousands of people a year: malaria alone killed 610 000 in 2024.

  • Only the female bites. Most mosquitoes need a blood meal to make their eggs; both sexes feed on nectar and plant juices.
  • Their metamorphosis is complete: egg, larva, pupa and adult. The larva and the pupa live in water, and so do the eggs of Anopheles and Culex. The larva moults four times before it becomes a pupa, which does not feed, having no mouthparts outside, and hangs from the surface by two breathing trumpets; the adult comes out of it at the surface.
  • The female's head carries a long proboscis, the mouthparts that pierce the skin; a pair of palps beside it, which sense the carbon dioxide that leads her to a host; and a pair of long antennae, finely haired in the female and bushy in the male.

In the diseases they carry, a mosquito can be more than a vector. Plasmodium's sexual cycle runs in the Anopheles female, so for malaria she is the definitive host as well as the vector. For Wuchereria, which only grows from microfilaria to infective larva inside her, the mosquito is the intermediate host and vector. For the viruses she is a vector in which the virus multiplies.

Anopheles and Culex compared

A medical biology course asks you to tell the two apart at every stage of their lives.

AnophelesCulex
Eggslaid one by one on the water, each with a float on either sidestuck together, standing on end, in a raft of 100 to 300
Larvano siphon; breathes through spiracles on its back, so it lies level just under the surfacea long siphon near its tail; hangs head down from the surface at an angle
Pupacomma-shaped, hangs from two trumpetsmuch the same
Female at resttilted to the surface, abdomen up, proboscis, head and body in one linebody level with the surface, head bent down
Female's palpsas long as the proboscisshort
Wingsusually spotted with blocks of dark and pale scalesclear
Breeds inmostly clean water: marshes, rice fields, the edges of streams and, for Africa's main vectors, small sunlit rain pools; the eggs do not survive dryingpermanent and stagnant water, ditches, drains, containers
Biteslate in the evening and at nightfrom dusk to dawn; some prefer birds
Carriesmalaria; lymphatic filariasis in the countrysideWuchereria bancrofti in towns; West Nile, Japanese encephalitis and other viruses

Two traps in the practical:

  • The palp rule works only on females. The males of both genera have long palps, club-tipped in Anopheles, and bushy antennae; a female's antennae are only finely haired.
  • Not every Anopheles has spotted wings. Most do, but some, such as the European An. claviger, have plain dark scales. The resting angle and the female's palps decide.

West Nile virus lives in birds, which Culex bites; people and horses are dead-end hosts, in which the virus does not reach levels that infect a mosquito. Culex pipiens spreads it in southern and central Europe in summer.

Aedes

Aedes mosquitoes are banded black and white and, unlike most others, bite by day. Ae. aegypti and Ae. albopictus lay their eggs on the inner walls of containers just above the water, in buckets, tyres, vases and anything else that holds a little, and the eggs survive drying out for up to 8 months. They carry the viruses of dengue, the most common viral infection carried by Aedes, yellow fever, Zika and chikungunya. Ae. albopictus, the tiger mosquito, has spread through much of southern and central Europe, where it has caused local outbreaks of dengue and chikungunya. Other Aedes species, such as Ae. polynesiensis, carry Wuchereria on the Pacific islands.

Control

  • Insecticide-treated bed nets and indoor residual spraying, insecticide on the inside walls where mosquitoes rest after feeding, are the two core ways of controlling malaria's mosquitoes. Resistance to insecticides is spreading in Anopheles, and newer nets protect better than pyrethroid-only ones.
  • Larval control: draining, filling or covering standing water, and larvicides. For Aedes, emptying the containers round the house.
  • Personal protection: repellents, long sleeves, screens on windows; against Aedes, by day as well.

Phlebotomus papatasi, the sand fly

The sand fly Phlebotomus papatasi
The female sand fly at rest on a surface, seen from the side, and below her on damp ground among fallen leaves her eggs, a larva and a pupa. She is small and pale, her body, legs and wings covered in short hairs. Her head is held low in front of a humped thorax, mostly taken up by a large dark eye; from it a long, slender antenna of many cylindrical segments curves forward and down, and below it hang a short proboscis and a longer palp that curls back under the head. Her lance-shaped wings are raised over her body at about 40 degrees, not folded flat. She stands high on six long, thin legs. The eggs are small dark ovals lying together on the ground. The larva is a slender grub with a black head, a pale body of twelve segments each carrying a feathery bristle, and two pairs of long hairs at its tail. The pupa stands upright, head up, its tail still in the crumpled last larval skin, from which the long tail hairs stick out.

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Sand flies carry Leishmania and the sand fly fever viruses. A female is only 1.5 to 3.5 mm long and hairy, with large black eyes and long legs, and rests with her wings raised over her body. Her young stages live on damp ground, never in water.

Simplified: the female and her young stages each drawn to their own scale; the body drawn simply in one muted colour, its covering of hairs shown as a few short lines; only the legs on the near side drawn; the antenna's segments and the wing's veins simplified.

3 sources
  1. European Centre for Disease Prevention and Control. Phlebotomine sand flies: factsheet for experts.
  2. Wikipedia. Phlebotomus; Phlebotomus papatasi.
  3. Galati EAB, Galvis-Ovallos F, Lawyer P, Léger N, Depaquit J. An illustrated guide for characters and terminology used in descriptions of Phlebotominae (Diptera, Psychodidae). Parasite 2017;24:26.

Phlebotomus papatasi is a phlebotomine sand fly, of the family Psychodidae, also in the order Diptera. It lives across the Mediterranean, North Africa, the Middle East, and Central and South Asia. Its relatives carry disease round the world: Phlebotomus in the Old World and Lutzomyia in the New.

  • The adult is tiny, 1.5 to 3.5 mm long, about a quarter the size of a mosquito, pale yellowish brown and hairy, with large black eyes and long, stilt-like legs. At rest and while feeding its hairy, lance-shaped wings stand raised over its body at about 40 degrees, which tells it from other small flies.
  • It flies weakly, in short hops close to the ground, and rarely goes more than a few hundred metres from where it breeds. By day it rests in cool, dark, damp places: cracks in walls, animal shelters, rodent burrows.
  • Only the female takes blood, mostly from dusk through the night, from people and many animals. Its mouthparts are short: it probes the skin and feeds from the small pool of blood that forms. Both sexes also feed on plant juices.
  • The life cycle is complete, like a mosquito's, but on land. The female lays 30 to 70 eggs after a blood meal in damp cracks in the ground or in walls, in animal burrows and among roots, never in water. They hatch in 4 to 20 days. The larvae, with a black head, a greyish body of twelve segments, feathery bristles and, from the second stage, two pairs of long tail hairs, feed on decaying matter such as fungi, dead leaves and animal faeces, and moult through four stages over 20 to 30 days. The pupa stands upright with the last larval skin still on its tail, and the adult comes out after 6 to 13 days.

What sand flies carry

  • Leishmaniasis. Sand flies are the only proven vectors of human leishmaniasis. P. papatasi carries L. major, which causes Old World cutaneous leishmaniasis, with rodents as its reservoir; although P. papatasi lives in southern Europe, L. major does not, for lack of those rodents. Around the Mediterranean, L. infantum, which causes visceral and cutaneous leishmaniasis, is carried by other Phlebotomus species, such as P. perniciosus, with dogs as its main reservoir.
  • Sand fly fever, also called pappataci or three-day fever: phleboviruses such as the Naples and Sicilian viruses cause a short fever with headache and aching muscles that clears in a few days. Toscana virus, also carried by sand flies, can cause a severe, occasionally fatal infection of the nervous system, in the summer months.
  • Bartonellosis, Carrion's disease, caused by Bartonella bacilliformis, is carried by Lutzomyia sand flies in the Andes of South America.

Protection

  • Avoid the bite from dusk to dawn: stay in screened or air-conditioned rooms, cover the skin and use repellent.
  • Sleep under a fine-mesh bed net, ideally treated with insecticide and tucked under the mattress: sand flies can pass through the holes of an ordinary mosquito net.
  • Spray insecticide indoors where the sand flies rest, remove their breeding and resting places, and put insecticide-treated collars on dogs where L. infantum is found.

Check yourselfAnswer, then say how sure you were: a lucky guess still counts as a weak point.

1In a pond you find mosquito larvae lying level just under the surface, with no breathing tube. Which genus are they?

2A female mosquito resting on a wall holds her body at an angle to the wall, her abdomen pointing away from it, and her palps are as long as her proboscis. Which disease could she carry?

3How do the palps tell a female Anopheles from a female Culex?

4Which feature tells a sand fly from other small flies?

5A traveller to Morocco asks how to avoid sand fly bites at night. What is the advice?