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The Genus Culex

Written by new sensation

By: Zoqia Tariq, Rameen Ansar and Sidra

Introduction

Culex is a genus of mosquitoes, several species of which serve as vectors of one or more important diseases of birds, humans and other animals. Culex is a small, dark mosquito that tends to feed on reptiles and amphibians. It is found in the southeastern United States and many countries in Central America and South America. It has not been identified as a species of medical importance as it has not been shown to vector pathogens like some other Culex species.

Diversity

The genus Culex is not only has one of the most dominant species and individuals but also one   of the most complex and difficult genera among the mosquitoes of Southeast Asia. In a recent preliminary study a rough estimate of between 120-130 species, both previously recognized and new, have been seen from the area. Genus of Culex is diverse in nature. Genus Culex comprises of over twenty subgenera   including a total of over thousand species.

Occurrence

Culex is recorded from many states and countries of the world including, Panama, Peru, French Guiana, Dominican Republic, Guatemala, Trinidad and Tobago, Paraguay, Puerto Rico and many of  United Kingdom. The species is also reported from Kentucky, as well as the eastern tip of Texas.

Physical Appearance

Culex mosquitoes tend to have relatively blunt-shaped posterior abdomens compared to other mosquito genera and are small and delicate (Marshall 2006). Female mosquitoes of the subgenus Melanoconion can be identified based on two unique features:

  • The thorax possesses a scutum lacking acrostichal setae.
  • The head has broad, flat scales posterior to the compound eyes.

Both sexes of Culex have dark short palps and a long dark proboscis, dark abdomen with somewhat reflective bronze or blue-green scales, dark thorax with a lighter patch on the dorsal portion of the mesepimeron, narrow and dark wing scales, and dark legs. As in all Diptera capable of flight, the second pair of wings are reduced and modified into tiny, inconspicuous halteres.

The male mosquitoes in the subgenus Melanoconion can be extremely difficult to identify to species, and an analysis of the genitalia is often necessary (Roth 1943). Positive identification of Culex females can be accomplished by observing only three teeth on the cibarial armature.

Life Cycle

Eggs: Culex pilosus females will lay their eggs near ponds or rainwater seepage areas and ditches which may or may not contain vegetation. Unlike other Culex eggs, Culexeggs lack a corolla (collar) at the anterior end of the egg. Another unique feature of this mosquito is that Culex pilosus lays eggs singly, or individually, or sometimes in single-layer patches, but not in rafts like many other Culex species mosquitoes. The eggs are placed just above the water line and are viable for one month in moist conditions.

Larvae: The larvae of Culex pilosus have a broad head and long antennae with a large tuft at the ends. On the ventral side of the larval head, an oval gill is inserted at the base of the antennae.  They have an upcurved siphon and a curved preapical spine at the end of the siphon. There are eight pairs of long tufts of setae on the siphon, comb scales on the eighth abdominal segment in a single row that appear long and pointed, and gills of two different lengths

Pupae: As with other mosquitoes, the pupae have two major body parts, a cephalothorax and abdomen. A pair of trumpets containing breathing spiracles is present on the cephalothorax. Culex pilosus pupae have abdominal segments with distinctive setae patterns; the second segment’s most medial seta possesses 14 or fewer branches. The pupal trumpet on the cephalothorax, which tapers gradually, is about four times as long as the width of the trumpet at the tip, and the pinnae are about one-third the length of the trumpet (Foote 1954).

Behavior of Culex

Culex adults tend to rest inside forests or woodlands during the day, but then fly over open land during the night to a different habitat in which they feed, only to return to their daytime habitat again in the morning. The flight patterns of adult Culex pilosus are not influenced by wind direction, which is unique among mosquitoes because many species tend to fly upwind. Culex feeds mainly on reptiles and amphibians.

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