All mosquitoes cause annoyance by biting but some mosquitoes are capable of transmitting disease from person to person. Three diseases may be carried in this way:
- Malaria by Anopheles mosquitoes
- Lymphatic Filariasis (elephantiasis) by the common house mosquito
- Dengue fever by the dengue fever mosquito
The common house mosquito and the dengue mosquito are both domestic species and will congregate in houses, whereas most anophelines will enter dwellings to bite and then return outdoors, until another blood meal is sought.
Mosquitoes either lay their eggs singly (Aedes and anopheles), or in rafts consisting of a hundred or more eggs (Culex), and their larvae or wigglers must develop subsequently in water. The eggs hatch usually in from one to three days, although those of some species (Aedes aegypti) can withstand desiccation for some months, and then quickly hatch when water is again available for breeding.
The larval or wiggler development takes about one week, and a pupal stage is then reached. In two or three days the pupa comes to rest at the water-surface. Its skin splits along the back, and the adult mosquito quickly emerges, hardens, and flies away. Female mosquitoes may live for several weeks, and females only are capable of taking blood meals.
1. Culex pipiens
The common house mosquito is widely distributed throughout the world. It is a night-biter, and a nuisance wherever found, as well as being responsible for the transmission of filariasis.
This species is grayish-brown and has unbanded legs. It is to be found during the day resting in dark corners, behind doors in cupboards, on curtains, or on clothing in the darker portions of the rooms.
It breeds in the neighborhood of houses, in any collections of water, preferably polluted, both on the ground and in artificial containers such as tins and flower vases. Drainage water, effluent from septic tanks, and drums containing liquid manure, are favored breeding places.
2. Yellow fever mosquito
The dengue fever mosquito is also known as the yellow fever mosquito. It has been associated with several widespread epidemics of dengue fever. Originally it was a breeder in tree holes, but has now adapted itself to breeding in artificial containers.
It is a domestic type and is not found far away from dwellings, preferring to breed in collections of clean water; it is commonly found in fire buckets, roof gutters, flower vases, tins, old motor tires, rainwater tanks, and in tree holes near dwellings.
This mosquito is very unobtrusive. It bites during the day as well as at night, paying particular attention to the back of the neck and ankles under tables. It is a small, black species with white-banded legs, lyre-shaped white stripes on the back of the thorax, and a dark proboscis.
3. Malaria mosquito
Mosquitoes capable of transmitting malaria may be readily distinguished by their attitude when resting or biting. The body and proboscis are held in a straight line, usually at an angle of 45 degrees to the resting surface, and on this account these species have been referred to as “dive bombers.” The wings bear scales, in many instances white, which give them a distinctive spotted appearance.
Breeding usually takes place in open shallow pools, along the weedy edges of marshes and creeks, and to a lesser degree in artificial containers. Each species has its own preferred habitat, and although most types prefer fresh water, some are capable of breeding in brackish water, such as may be found in mangrove swamps.
As mosquitoes must breed in water, control, particularly of the domestic types, must first be directed at the elimination of all possible breeding sites.
If control programs against a specific mosquito such as the dengue fever mosquito are being considered, artificial containers, fire buckets, roof gutters, water tanks, etc. would need attention, whereas ground water would be unimportant. Drains, swampy areas, etc. would require treatment, however if the common house mosquito were involved.
Tanks should be effectively screened with wire gauze (18 mesh to the inch) or other mosquito-proof material. Fire buckets and other water containers should be emptied weekly, and care taken to ensure that wigglers do not cling to the sides of the vessel.
Permanent water may be treated by oiling with kerosene or special oils, at least once a week during the summer months. Two tablespoonfuls of kerosene will cover 15 square feet of water, and if castor oil (1 part) is added to the kerosene (50 parts) the surface film spreads better and lasts longer. This treatment kills all wigglers and pupae as they come to the surface of the water.
Adult mosquitoes may be killed by the use of kerosene pyrethrum sprays as used against house flies. Concentrated (4 percent) DDT sprays applied for residual action against house flies, will also give equally good results against mosquitoes.
Effective mosquito repellents are now available and of these, Dimethyl phthalate, the repellent used in the army, is recommended. A small amount of the liquid is placed on the palms of the hands and then carefully smeared over all exposed parts of the face, neck, hands and arms. A second application is usually necessary after two hours where heavy infestations occur.
Dimethyl phthalate must not be rubbed into the eyes, on the lips or other sensitive areas, as it may cause an intense irritation. This repellent will dissolve plastics and must be kept away from spectacle frames, fountain pens, unbreakable watch glasses etc.