House flies

(Musca domestica and Musca vicina)

House fly is larger insect, 6-7 mm long, greyish with blackish markings and with a wing span of 13-15 mm and having two wings, posterior wings modified in a pair of halteres or balancers. Wings when folded over the abdomen at rest diverge posteriorly.

Mouth parts are sponging type or haustellate, which are adapted to feed on liquid diet only. When they have to feed on solids such as sugar crystals, they first vomit the contents of stomach over it and dissolve food in it before swallowing. Eyes are very large, covering major part of the head and antennae small aristate. They are very agile and expert fliers, capable of landing upside down on the roof. They can fly up to 80 feet high. Adult longevity is generally 2-3 months but may be reduced to 2-3 week in hot weather.

Houseflies breed in cow dung heaps, filth, compost and other decaying matter that has a lot of moisture content. Fecundity is 700-950 eggs/female. Eggs are laid in about 6 batches spread in 3-4 days and placed beneath the surface of the medium. Adults can survive for 1-3 months. Eggs are creamy white, elongated, 1 mm long and 0.25 mm wide. Incubation period ranges between 12 and 24 hours but in summer eggs can hatch within 6 hours.

Larva is called maggot, is creamish in colour, narrow anteriorly and broad posteriorly and truncated. There is no distinct head anteriorly but a distinct black spine or oral hook that helps in feeding and moving about in filth. Anterior part of thorax contains a hard chitinous cephalopharyngeal skeleton. On the posterior end of the abdomen there are a pair of spiracles located in a pair of D-shaped depression. Full grown larva is 1.25 mm long. There are 4 larval instars and the larval period is 5-10 days depending on the temperature. Larva feeds on decaying organic matter and avoids light and high temperature. For pupation the larva has to migrate to drier place or compact soil.

Pupa is barrel shaped, dark brown and shorter than the larva. Posterior end has two spiracles for breathing. Pupa is a dormant stage but can move vertically up to one foot to reach near the surface before adult emergence. Pupal period is 3-5 days but can be less in hot weather. The entire life cycle may be completed in 8-16 days.

Diseases transmitted by housefly

MODE OF TRANSMISSION

Housefly transmits diseases in two ways:

1. External carriage: When housefly sits on filth and dung etc., pathogenic organisms get attached onto the lower side of oral disc, hairs of tibia and tarsi and on abdomen. When the same fly sits on food items meant for human consumption, the pathogens are release into it and get into the human system through contamination.
2. Internal carriage: In this mode pathogens are swallowed and retained in the gut. Housefly has a habit of regurgitating stomach contents on the food material before swallowing it. It also defecates frequently in the form of fly specks. As the alimentary canal of house fly contains pathogens, in both ways it releases pathogens in the articles of human consumption. Even utensils containing fly specks can transmit pathogens if not washed properly.

CONTROL OF HOUSE FLIES

Removal of breeding places: Cow dung and other manures should be removed and buried in special pits and covered with soil. In dairies proper drainage system should be installed so that hygiene and dryness could be maintained. Household refuse should be kept in covered bins and not dumped in the surroundings. Maintenance of cleanliness is an effective method to bring down house fly population.

Treatment of breeding places: Where it is not possible to remove garbage heaps and cowdung immediately, it should be covered with a layer of insecticide dust such as 5% DDT or BHC dust to prevent flies to feed and lay eggs. Pyrethrum and neem oil can also be used in rural areas.

General precautions: Windows and doors should be made fly proof by covering them with wire mesh. Food material should be stored inside covered almirahs, fridges or covered containers. Eating utensils should not come in contact with flies or should be washed again before use. Particular care should be taken where large scale cooking is done as in marriages and parties.

Control of adults: Adults can be killed by spraying insecticide such as Baygon, malathion, lindane, endosulfan, carbaryl or synthetic pyrethroids. Sugar baits containing the above mentioned insecticides are quite effective in killing adults. UV emitting electrocuting traps are quite effective in attracting and killing adults and can be commonly seen in shops and restaurants.

Biological control: Fowls scratch the soil and manure with their legs and feed on the maggots of houseflies. A pupal parasite, Spalangia, has been found to be very effective in destroying pupae of houseflies.