Subfamily: Phlebotominae (sandflies)

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Sandflies (Phlebotominae) are blood suckers and their larvae inhabit places where there is high organic matter such as in animal burrows, termite hills and tree holes. Sandflies are best known as vectors of trypanosome species in the genus Leishmania, causing diseases collectively known as leishmaniasis.

Identification

Sandflies belong to the fly family Psychodidae, members of which are characterised by their densely hairy wings which give them a moth-like appearance. Phlebotomines are distinguished from other members of the family by the way they hold their  wings above the body in a vertical V (see picture of member of other subfamily showing how wings are held flat near the body).

Diversity and distribution

There are about 700 species of phlebotomine sandflies of which about 70 are considered to transmit diseases to people. The term sandflies is also sometimes confusingly used for other small biting flies, especially ceratopogonid flies of the genus Culicoides. It is used below exclusively for the Phlebotominae. Sandflies are found mainly in the tropics with a few species also found in the temperate regions. They occur in a wide range of habitats and species often have very specific habitat requirements. In the Old World, leishmaniasis is found mainly in dry, semi-arid areas whereas in the New World, this disease occurs mainly in tropical forests and savannas. 

Classification

New World sandflies

  • Genus: Brumptomyia
  • Genus: Lutzomyia. The only genus of phlebotomine flies that suck blood from people in the New World.
  • Genus: Warileya

Old World sandflies

  • Genus: Phlebotomus. The main genus of phlebotomine flies that suck blood from people in the Old World and the only genus of phlebotomine flies that transmit diseases to people in this region.
  • Genus:

    Sergentomyia. Feeds mainly on reptiles, sometimes transmitting the protozoan parasite Sauroleishmania. Rarely bites people and does not transmit diseases to people. 

Disease organisms transmitted

  • Leishmania. Protozoan parasites that cause visceral leishmaniasis (kala-azar) and various types of cutaneous leishmaniasis (e.g. oriental sore, espundia) in people.

  • Bartonella bacilliformis. A bacterium causing the disease bartonellosis (Oroya fever, Carrion's disease) in northwestern South America (Peru, Colombia and Ecuador).

  • Sandfly Fever Virus. Transmitted by sandflies in North Africa and the Middle East.
  • Toscana virus. Occurs in the northern and western Mediterranean.
  • Chagres and Punta Toro viruses. Occur in the New World.

Life Cycle

It is difficult studying the life cycle of sandflies because the larvae are tiny and don't live in well defined places, like mosquito larvae. The entire life cycle takes 20-40 days except in diapausing species (i.e. those that stop developing when conditions become too cold).

Eggs. The female lays 30-70 eggs by scattering them around a potential breeding site. They hatch within 1-2 weeks.

Larvae. Larvae feed on dead organic matter and are found in damp places containing organic matter such as cracks in walls or rock, animal burrows and shelters, caves, or in leaf litter. In regions with cool winters, larvae diapause in the fourth (final) instar.

Pupae. Pupal development takes 5-10 days.

Adults. Emerge from the pupae in darkness, often just before dawn. Only the female sucks blood, the food being used for egg production. Both males and females feed on sugary secretions from plants or from honeydew produced by homopteran bugs. Mating takes place at or near hosts: the males congregate in leks on or near the host and produce sex pheromones. Females home in on hosts using both host odour and the odour produced by the males. Vibration of the wings by males can be important in encouraging females to mate. 

Adults are mainly active in the early morning, evening and at night although they can bite during the day if disturbed. When innactive, adult sandflies have habitat-specific resting sites that are characteristic of particular species. One of the main ways in which entomologists study sandflies is by locating and studying them at their resting sites. Resting sites are often similar or near to the larval breeding sites and are usually places that are cool, humid and dark. Sandflies are able to survive in dry environments by withdrawing to cool, humid resting sites during the day and then becoming active at night when ambient temperatures drop and humidity increases. 

Seasonal activity of adults is affected mainly by temperature and rainfall.

Control

  • Spraying of residual insecticides on surfaces in the home. This has been the main way used for controlling sandflies but is obviously ineffective for those species which bite away from the home such as those in South American forests. This control technique is also used for killing Anopheles mosquitoes that transmit malaria and is some regions it is effective in reducing both malaria and leishmaniasis.
  • Killing of reservoir species. Certain species of mammals can act as important reservoirs of Leishmania and by killing the reservoir species that are living near human habitation, disease rates can be decreased. For instance, rodenticides have been used against the Great Gerbil Rhombomys opimus in Central Asia.
  • Insecticide spraying of larval habitat. This is usually not possible because, usually, so little is known about where the larvae occur.

References

  • Lane, R.P. 1993. Sandflies (Phlebotominae). In: Medical Insects and Arachnids (eds R.P. Lane and R.W. Crosskey). Chapman and Hall, London, pp. 78-119.

 

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