Introduction
Blowflies and Houseflies
Control of flies
Flies in fishmongers’ shops can be both repulsive and dangerous. Not only can they cause customers to turn away but, since most flies feed and breed in decaying materials, they carry disease organisms that can be transmitted to man by infected food.
With customers becoming increasingly discerning and having more regard for hygiene and quality the good name and reputation of the fishmonger can be irrevocably damaged through the sale of fly-infested fish. The costs of defending a legal action brought against the vendor of contaminated food can be high.
It is not always practicable to eliminate flies completely from a shop, but much can be done to keep down their numbers, prevent breeding and make the premises generally less attractive to them.
This note describes some of the precautions that can be taken to keep shops free from flies.
Of the various flies that infest fish shops, the most troublesome are the different kinds of blowfly, namely bluebottles (Calliphora), greenbottles (Lucilia) and black-bottles (Protophormia). They lay their eggs in batches of ten to three hundred on fish, fish waste, poultry or game, and in a very short time, varying from a few minutes to a few days, the eggs hatch into maggots, often called gentles, which feed for several days. The fully-grown maggots usually crawl out of the food and burrow into the ground or into cracks and crevices. They then pass through a resting stage, called the pupa, and finally emerge as adult blowflies. The entire life-cycle, from egg to fly, may take as little as nine days during hot weather.
The housefly has a somewhat similar life-history, but is unlikely to breed on the premises. It breeds in such materials as dung, fermenting vegetable waste and domestic refuse.
Flies are most troublesome in warm weather but they persist in small numbers throughout the year.
The control of flies at fishmongers’ premises must include preventive measures both inside and outside the shops. It is strongly recommended that at each shop one person should be made responsible for all hygiene and control measures.
Indoors
1. HYGIENE
Floors should present a hard, smooth surface with no awkward corners; the angle between floors and walls should be coved. Floors should be thoroughly washed down at least once a day, and no fish waste should remain trapped in corners or on drain covers.
Display units and containers should be kept covered and the contents kept chilled; this will reduce attractive odours and prevent flies getting on the fish. Pish in open-topped, chilled cabinets are (not is) vulnerable to fly attack; and eggs and maggots, although inactive, are not killed at low temperatures.
Offal buckets should be emptied and scrubbed out at least once a day.
Fly screens of wire or nylon gauze of 2 mm mesh-hole size may be fitted over windows and other openings.
2. INSECTICIDES
It is unwise to apply insecticides while foodstuffs are exposed.
Persistent insecticidal films can be applied to the interior surfaces of the shop and will give some control of flies settling on the ceiling, walls, etc. There is some risk, however, of partially paralysed flies falling on unprotected goods. Plastic strips impregnated with dichlorvos can be hung in the shop and adjoining rooms. These strips emit insecticidal vapour which in enclosed premises can give continuous control for several weeks. There is again some risk that partially paralysed flies will fall on to the food on display.
After the shop has been closed each night and all food stored away, the premises should be completely cleared of flies by spraying with an insecticide such as pyrethrins or dichlorvos. Either an aerosol dispenser or an efficient hand sprayer can be used. The hand sprayer should give a fine spray with no large droplets.
After the nightly spraying, all surfaces on which food will be placed must be thoroughly scrubbed and then hosed down. Most detergents can be used, provided the surfaces are properly swilled afterwards. Wooden bench tops should be scrubbed with a hypochlorite wash containing 600 parts per million of free chlorine, that is one egg-cupful of commercial sodium hypochlorite solution in a gallon of water.
Outdoors
1. HYGIENE
The highest possible standard of hygiene must be maintained everywhere.
Floors of all yards and outhouses should be of smooth concrete sloped towards the drains and should be liberally hosed, at least once a day.
Drains should be kept clean. Inspection covers should be bedded in grease and correctly fitted. Gully and channel gratings should be lifted at least twice a week and scrubbed on the underside; the channel and rebate for the grating should also be scrubbed.
Offal bins should have heavy, tightly fitting lids with a deep lip, and should always be kept covered. They should be stored in closed outhouses and not left exposed in an open yard. If they must stand in the open, the plinth and backing walls should be sprayed with insecticide in the manner described below. All offal should be disposed of quickly; it should never remain on the premises for more than two days, and if possible should be collected daily. The bins should be washed out after emptying.
Fish boxes should be scrubbed out with detergent solution as
soon as they are empty, rinsed with hypochlorite solution and stacked on end to
dry. The dry boxes should be stored as far as possible from the shop, preferably
under cover, and disposed of as soon as possible. For ordinary wooden boxes, the
hypochlorite rinse should be fairly strong, made by adding 5 pints of commercial
hypochlorite solution to 8 gallons of water; for aluminium boxes use about
pint of commercial solution
in 8 gallons of water.
2. INSECTICIDES
A suitable insecticidal solution for spraying outside premises can be prepared using either malathion, fenitrothion or iodofenphos diluted to 1·5% with water.
The outside of all bins, and both sides of the lids, should be sprayed with this solution once a week, using a hand pump. If the bins are kept in the open, the plinth and backing wall should also be sprayed at the same time.
Walls and fences around the yard should be sprayed fortnightly with the same solution.
Neighbouring Premises
If flies appear to come from premises nearby, the occupiers should be asked to cooperate by adopting similar control measures. If necessary, the environmental health department of the local government authority should be consulted.
Precautions with Insecticides
ALWAYS READ THE LABEL before use.
Use only insecticidal formulations labelled as suitable for controlling flies.
Store insecticides away from foodstuffs and only in labelled and tightly-closed containers.
Keep insecticide off the skin (wear p.v.c. gloves), avoid breathing sprays, wash hands after use.
Prepare spray solutions outdoors away from food.
Do not allow insecticides to come into contact with exposed food, food utensils or surfaces on which food is prepared or stored.
Extinguish all naked flames before applying sprays or aerosols.
Securely cover or remove tanks containing live fish before using insecticides.
This note has been prepared with the assistance of the Pest
Infestation Control Laboratory of the Ministry of Agriculture, Fisheries and
Food.
