Family: Culicidae

Mosquitoes (Culicidae)

The female mosquito is the only stage that "bites". Most require a blood meal to produce a full compliment of eggs. They will also feed on nectar, as do the males. People are well acquainted with female mosquitoes but rarely see the males unless they are in mating swarms. The sexes can be easily distinguished. Both have densely scaled bodies, legs and wings. The females have a long proboscis and sparsely haired antennae. The males have a proboscis, bushy antennae, tufted palpi and the end of the abdomen is modified into external genitalia.

The life cycle includes four stages; egg, larva, pupa and adult. Eggs are laid directly into the water or in damp soil in groups or singly. In many species the egg has a "resting stage" known as diapause that prevents the eggs from hatching until the following spring. Other species have more than one generation a year. Some species have desiccation resistant eggs that enable them to withstand consecutive years of drought. Such species can successfully inhabit shallow depressions that contain water for only a short period of time at irregular intervals such as ditches and temporary ponds. The eggs hatch into larvae.

The larvae of most mosquitoes feed on microscopic algae and small organic particles that they filter from the water. They are commonly called "wigglers" which describes their characteristic method of swimming. Larvae pass through 4 growth stages (instars) and then turn into pupae. The pupal stage is a period of major tissue reorganization as the adult body structures develop within it. When the pupal stage ends it swims to the water surface and a split develops along the top of the skin and the adult emerges and flies away.

Identification of adult mosquitoes relies on morphological structures, color patterns of microscopic scales on the abdomen, legs and thorax, coloured hairs on the thorax and claw shapes. The taxonomic keys have been developed using reared specimens that are in pristine condition with a full compliment of scales and hairs. As the adult ages scales and hairs are lost from the body making it very difficult to impossible to accurately identify older specimens.

Over the past few years West Nile Virus has been in the news and of great public concern in SK. The main human vector for the virus in Saskatchewan is Culex tarsalis. An image with diagnostic characters and a brief biology is provided below.

Culex tarsalis DIAGNOSIS: Hind tarsal segments with apical and basal bands of pale scales. Proboscis with a broad median band of pale scales. Third and fourth palpal segments with pale scales. Abdominal segments with a basal band of pale scales. The remainder of each abdominal segment dark scaled. Wings predominantly dark scaled except for a few pale scales at the base of the costa and some on the subcosta. BIOLOGY: Usually larvae are found in permanent and semimpermanent ponds. But they can be found in temporary ponds and even hoof prints in midsummer. The female is the overwintering stage. They survive in caves, burrows or rock piles. Females feed on birds but will also attack mammals this makes them an ideal vector for WNV to humans. There can be as many as four generations per year in the southern parts of the province if conditions are favourable. It can also be a vector of Western equine encephalitis.