Flies bred for tests

Press, 27 June 1987, Page 21

Flies bred for tests

Phtt ... phtt ... die, you little ... (and still they come)

BY

SUZANNE KEEN

At a time of year when most people are thankfully shutting their doors on the household fly, the Consumers Institute Laboratory in Christchurch is running a breeding programme to yield at least 30,000 of the parasites. Laboratory staff are tackling their first live breeding experiment, in which third-generation flies are being used to test the efficiency of various brands of fly killers. The laboratory head, John Pollard, says that to begin with, each staff member was sent home with a small container and asked to capture five flies. “Each test or squirting requires 600 good, fresh flies, bred from a collection of stud house flies which were gathered around Christchurch,” he says. The task sounded simple enough, but for the initiated fly catcher there was a trap. Seven breeds of fly exist in New Zealand, and it takes an expert , eye to distinguish the Musca Demestica (housefly) from its numer-. ous relations.

The staff member in charge of fly breeding, lan Orchard, says that if a person did go down to the city dump to capture the insects, there is no guarantee they would get the genuine housefly. A breed commonly confused with the housefly is the false stablefly. Mr Orchard says it is important to eliminate that fly from the experiment, since it does not breed with the housefly, and does not comply with the required national standards for testing fly killers. The laboratory enlisted the help of an entomology consultant, Dr Roy Harrison, who sorted the flies, removing five false stableflies from the hand-picked breeding stock. They have

slightly different coloured hairs on their abdomen and different shaped veins on their wings. Mr Orchard put the 15 houseflies in a container, and the eggs he collected from them in small pots of larval medium. The mixture consists of bran, soya flower, mixed vegetables, malt and yeast. After about a day, the maggots emerge from the eggs. In another fortnight, they reach the pupa stage. Mr Orchard then spends hours confined to the 27deg. room, separating the pupa from the larval medium with a spoon.

The slightly putrid smell which exists in the small space does not bother this dedicated man, who has lost count of the pupa he has collected. “It’s the maggot droppings themselves that smell, not the maggots,” he says. Any flies escaping from the breeding stock or prematurely developing from pupa to fly about the room are brought to an abrupt end by a pest strip suspended from the roof. lan Orchard places the washed and dried pupa in suspended animation in the refrigerator until they are needed for testing the fly killers. This is a normal state for the insect, which usually winters-over' in suspended animation. When they are needed to test the fly-killers, the pupa are removed from their

eight to lOdeg. habitat and thawed out. After a few days, they emerge as flies, but it is another five days before they

can be used in the experiment. The testing room is bare and rectangular-shaped, with washable walls and a newspaper-

covered floor. Mr Orchard says the room must be warm and “not too bright” during testing. The flu-

orescent lighting tubes have to be placed outside to prevent the insects becoming trapped in them.

“We release about 600 flies in the room, then walk down the length of it running the flyspray can for so many seconds.”

Two staff members must then stand back-to-back in the room, counting how many flies drop each two minutes. At the end of 10 minutes, a count is made of any still flying. Aerosols have a paralysing effect which knocks the insects out, and at least 50 per cent of the flies must be brought down in the first six minutes.

An extractor fan removes any traces of spray from the room at» the end of each test.

“We then vacuum up the ones on the ground, put them back in the cage, and nourish them on sugar and water,” says Mr Orchard. The vacuum cleaner is specially adapted to suck the flies into a plastic bottle without damaging them, and the sweet reviving mixture is intended to test the long-term effectiveness Of each fly killer. “People say they often spray and the flies die, but 10 minutes later they come back to life and fly around. They are probably right, but they should come dead within 24 hours.”

Mr Orchard says another count is made of the flies 24 hours after the test spray. For a fly killer to meet the national standards, at least 99.5 per cent of the

insects must be dead. “The laboratory will also be testing the more permanent effects of fly eradicators,” says lan Orchard.

Fly killers being tested comprise nine aerosols, one fly paper, two pest strips, four electrochemicals and two electrocutors.

Each aerosol must be tested six time, each test using at least 600 flies.

It bears remembering that the laboratory began its experiment with only 15 flies. Several weeks and two generations later, it will be abuzz with upward of 30,000 flies, more than enough for the required testing. A four-day holiday by Mr Orchard had no detrimental effects on the experiment, he simply lowered the temperature in the breeding room a few degrees and slowed the process down. “You’ve got to admire them," he says. “They are a very efficient animal and have been around for a very long time.” He is surprised at the number of second generation flies which lived for more than a month.

John Pollard says that all the laboratory staff, some of whom are involved In testing light bulbs, car tyres and roof paints, had learned a lot about flies.

Most even know the easy way to distinguish a male fly from a female.

“The females have a wider space between their eyes. There is another method, but it requires very accurate eyesight,” says Mr Pollard. The staff will have only about one day between the time the fly experiment is disbanded and a new experiment begins — testing the stretchability and run-resis-tance of pantyhose.,