Flies and Fly Control – New Zealand
There are many species of fly in New Zealand. Most pose a threat to hygiene and are a nuisance to humans and animals. Some, such as Sand Flies, are a direct irritant, biting humans and sometimes causing painful reactions. The term ‘flies’, for the purposes of this discussion, includes all flying insect pests except wasps and bees (discussed elsewhere). Such insects include common pests like houseflies (Musca domestica), blowflies (Calliphora spp), cluster flies (e.g. Pollenia rudis), clothes moths (Tineola bisselliea and T. pellionella), midges and crane flies (Tipula paludosa).
The flies encountered in urban and industrial premises can be of many types, but it is generally accepted that those which are regarded as pests are those which spread disease through contamination, cause physical damage and are a general nuisance.
The insects most associated with the spread of disease in domestic, commercial and industrial premises are the true flies (Order: Diptera). There are many thousands of species of flies, however, relatively few interact with humans. Those that do are among the most destructive of pest species, spreading disease to man and domesticated animals, as well as contaminating food.
Adult flies fly. It is this that makes their status as pests so important, allowing them mobility to visit many diverse habitats. By nature, many flies breed and feed in areas of unsanitary conditions, with larvae feeding on decaying organic matter. The adult female uses complex sensory systems to choose suitable areas of rotting vegetation and decaying animal matter in which to lay her eggs and for the larval stages to develop into pupae. The adults emerge from the pupae in these unhygienic sites and, as they do, they become contaminated with disease-causing organisms. They may fly to sensitive food preparation, processing and consumption areas, seeking feeding sites for themselves as adults.
The likelihood of contamination of human food with pathogens has been proven over the years by a number of experiments. In these, disease-causing agents have been found to survive on outside body surfaces of flies. They also exist in the gut and blood system.
Flies are fluid feeders and, although they feed on solids, they need to liquidize the food before they can suck it up. They do this by producing large quantities of saliva from their salivary glands. This is then poured onto the food via the salivary canal of the mouthparts. The flies also frequently vomit some fore-gut contents onto the food while feeding. In addition, during the feeding process, flies frequently defecate. This in turn can spread pathogens from the hindgut of the fly onto food and food preparation areas.
If the food on which the flies have been feeding and defecating is prepared for human consumption, human disease and suffering is frequently the result. Food poisoning outbreaks can occur from a minute dose of pathogens and it is common that flying insects spread disease.
The housefly and the blowfly belong in the order Diptera (two-wings) that contains over 100,000 species. The female fly lays her eggs onto a suitable food medium, rotting organic material for the housefly and all types of meat for the blowfly. The eggs will hatch after a day into a maggot. It is the blowfly maggot that anglers often use as bait. The larval stage takes about a week to complete, it is followed by the pupal stage, and after a further 1-2 weeks the adult fly will emerge. Very large infestations can occur given the right (or wrong) conditions.
Cluster flies are large flies (10-15mm), with a dark gray to black non-metallic abdomen. In late autumn and early winter they will move into homes and other buildings to over winter. They are named cluster flies because of their habit of congregating in large groups in dark places such as attics. They release a pheromone (smell) that attracts others. This pheromone will linger on even after all the flies have been destroyed and removed and will continue to attract flies so that the clusters keep recurring. It is there fore important that treatments are continued even when there are no flies present.
Midges in New Zealand are native flying insects associated with water such as lakes and are often referrred to as Lake Flies. The adults are 5-10mm in size and do not bite, having no mouth parts. The adults only live for around 36 hours, however they can become a considerable nuisence when they congregate in large numbers during warm weather. They may be seen in large clouds around lakes and will be attracted by lights and settle on light coloured surfaces. The larvae of midges are known as blood worms and feed on decaying matter found on lake beds.
Fly Control Methods
The treatment and prevention of flies relies first on an accurate identification of the pest species. Only then can an effective strategy be tailored to the elimination of the source of the fly infestation, the prevention of flying insects entering the affected areas and the destruction or removal of any insects present. Control measures might include, interior and exterior surface treatment with long lasting insecticides, proofing with mesh and chain curtains, Target Pest fly trap unit ultra-violet (blue light) insect traps, and housekeeping. Target pest recommends combining fly and spider proofing as a single treatment. The control of flies has the effect of removing the food source for many spiders and the control of web building spiders reduces the food source for Whitetail spiders.