Order: Diptera (‘two-winged’)
- Single pair of membranous wings
- hindwings modified as halteres
- suctorial mouthparts, piercing or non-piercing; large compound eyes
- tarsi, 5-segmented
- metamorphosis complete with egg, larval, pupal and adult stages.
Lesser Housefly (Fannia canicularis)
Description: Lesser Housefly
- Adults, 6mm long with 12mm wingspan
- grey thorax with 3 longitudinal stripes, less pronounced than those of Common housefly
- extensive yellow patch at base of abdomen
- at rest, wings are folded along back
- venation shows 4th vein extending straight to wing margin
Lesser houseflies (Fannia canicularis) are frequently encountered in poultry houses.
They have an erratic flight pattern and are often seen flying in large numbers around indoor light fittings or other centre pieces.
The Lesser housefly is more tolerant of cool conditions than the Common housefly.
This species survives the winter mainly in the form of pupae, although, as with the Common housefly, adults remain active and reproduce throughout the year in warm conditions.
Life-Cycle of the Lesser housefly
Lesser houseflies are prolific breeders in poultry manure, but will also breed in other moist decaying matter. Egg laying commences when the female is 10 days old. The eggs are banana shaped, 1mm in length and bear a pair of longitudinal ridges which assist flotation in a liquid medium.
The flattened, legless, greybrown maggots hatch within 24-48 hours.
Hairy protuberances on their dorsal surface are thought to aid progression and floating in a semi-liquid medium.
The newly hatched larvae frequently wander for a time before burrowing into a suitable food.
Larval development requires a minimum period of 8 days, during which time the larva passes through 3 stages, eventually attaining a length of 6mm.
Pupation requires a drier location and lasts for at least 10 days.
Development from egg to adult emergence takes 3 weeks, although cooler conditions prolong this period.
Significance of the Lesser Housefly
Lesser Houseflies can transmit intestinal worms, or their eggs, and are potential vectors of diseases such as dysentery, gastroenteritis, typhoid, cholera and tuberculosis.
They will frequent and feed indiscriminately on any liquefiable solid food, which may be moist or putrefying material or food stored for human consumption.
Lesser Houseflies liquefy food by regurgitating digestive juices and their stomach contents on to the food substance. This ‘liquid’ is then drawn up by the suctorial mouthparts and in so doing the insects pick up pathogenic organisms. These may collect on their bodies and be transferred on contact with other surfaces or survive passage through the gut to be deposited as fly spots.
Fly spotting, produced when the insect feeds or defecates, results in rejection of contaminated farm produce, for example eggs, at point of sale.
Flies are frequently the subject of complaints to environmental health authorities, causing major problems where infestations overspill from breeding sites such as rubbish tips and animal houses.
The Lesser housefly makes longer flights and spends less time resting than the Common housefly.
Females of the Lesser Housefly species tend to remain near the breeding sites and only the males migrate.
For these reasons Fannia canicularis is less prone to transmit disease than Musca domestica (Common Housefly), but large populations and similar feeding habits mean that this insect, too, has a considerable potential to act as a vector of disease. It has occasionally been implicated as a vector of intestinal or urinary myiasis.
Control of Lesser Houseflys
Lesser Houseflies have rapid, prolific breeding habits and high mobility. In order to break the life-cycle, control measures should be directed against larval and adult flies.
Satisfactory hygiene is necessary to limit potential breeding sites and food sources.
Domestic refuse should be stored in well sealed bins, for early removal to disposal sites.
High-risk material should be sealed in bags and burnt wherever possible.
Refuse tips should be covered with earth, to a depth of at least 230mm (9 inches), and then compacted, this will minimise larval emergence and promote fermentation temperatures at which larvae cannot survive.
Farm manure should be kept as dry as possible, especially in poultry houses, where leaking water feeders can provide ideal, moist breeding conditions.
The Biothermic method of storing dung involves compacting manure into a cuboid stack, a method particularly suited to horse manure. This form of storage promotes uniform, persistent fermentation throughout the dung, which is lethal to larvae. Tarpaulins can also be used to cover heaps, in order to prevent egg laying and conserve the heat of fermentation.
Entry of adult flies into buildings can be prevented by 1.18mm-mesh fly-screens (which can easily be removed for cleaning), air curtains, bead screens or self-closing doors equipped with rubber flaps.
Physical control using maggot traps
Maggot traps take advantage of the fact that larvae need to migrate from breeding sites to cooler surroundings in order to pupate. A simple trap consists of a concrete platform, on which manure or refuse is stored, surrounded by a water-filled moat in which migrating larvae are trapped.
In order to obtain the best results, insecticidal control measures should be integrated with good hygiene.