|Mosquitoes and Flies|
Mosquitoes and flies
This article focuses on the control of mosquitoes and houseflies. Many pesticides used contain active ingredients with associated environmental and health effects.
The housefly (Musca domestica) and mosquitoes (Aedes, Anopheles and Culiseta) are ‘true flies’ and belong to the order Diptera, meaning two winged.
Female mosquitoes transmit disease by their habit of feeding on human or animal blood. Male mosquitoes only feed on sap or nectar and so do not carry the same threat. Females lay eggs on sheltered water as larvae need water to survive using air tubes protruding through the surface of the water to breathe.
Female mosquitoes rest on sheltered water using surface tension to lay their eggs. Although water is crucial to the survival of larvae a surprisingly small amount will suffice. Care should be taken to remove or pierce all containers that can potentially hold water in the garden, discarded pots and tyres make ideal breeding grounds.
Encouraging and introducing natural predators such as frogs, tadpoles, dragonflies, spiders, birds and goldfish into the garden will help to control mosquito populations. Carp and tench (Cyprinidae), sticklebacks (Gasterosteidae), goby (Gobius mocrops) and rudd (Scardinius erythrophthalmus) are examples of European mosquito-predaceous fish(1).
Repellents are not designed to kill insects and many are therefore not covered by the Control of Pesticides Regulations (1986). However, manufacturers bringing new products or active ingredients onto the market from May 2000 will have to apply to the Health and Safety Executive for registration under the EU Biocidal Products Regulations 2001(2).
Chemical insecticides cause problems with population resistance and can also cause population explosions due to the reduction of non-target species which are natural predators. Mosquitoes also perform an important part of aquatic ecosystems and their complete removal will cause habitat disruption. The traditional and widespread application of DDT killed adult mosquitoes but also affected other beneficial insects, birds, fish and natural predators(3).
Essential oils are regarded as being less toxic repellents than those containing synthetic chemical products(4). Citronella candles for outdoor use are available but the heat from the candle may cause the scented smoke to rise too high or in the wrong direction to be effective.
Flies can enter buildings by flying down chimneys but can be deterred by fitting a removable cardboard sheet as a barrier to entry during summer. Domestic waste should be kept wrapped and covered until collected to prevent adults feeding and laying eggs.
Biological control products aimed at controlling fly populations are not suitable for domestic situations but may be useful to control problems associated with animal husbandry or stables.
Flying insect sprays do little to control fly populations and emit pesticides into air breathed by people and pets. Fly and mosquito control active ingredients and their environmental and health effects are listed in Table 1.
Aircraft spraying against insects
US air passengers have complained to the Environmental Protection Agency (EPA) of headaches, nausea, fatigue, seizures, and in extreme cases, memory loss or a depressed immune system. A passenger suffering from emphysema died of ‘acute exacerbation of chronic airways obstruction’ 18 hours after being sprayed with d-phenothrin on a flight to Australia(5).
British Airways spray a pesticide product, containing the active ingredient d-phenothrin, an isoparaffinic solvent and an HFC propellant, within passenger aircraft cabins on more than 30 routes worldwide to comply with the World Health Organisation’s International Health Regulations (1969).
Australia requires incoming aircraft to be sprayed on the ground before boarding. However, if the treatment expires before returning to Australia then spraying may take place whilst passengers and aircrew are present(6).
Mosquitoes and flies can be irritating to us and may be vectors of harmful diseases at home and abroad. There are a number of non-chemical precautions that can be taken at home to control populations which are easily incorporated into domestic routines. Fly sprays will do little to control flying insect populations but will increase the toxicity of indoor air quality. Mosquitoes may be more of a problem when travelling abroad and care should be taken to choose the least toxic repellents and to enquire about airline policy in relation to pesticide treatments on aircraft. (AW)
The main sources for this article were:
J French, Organic Control of Household Pests, Aird Books, Melbourne, 1990.
W Olkowski, S Daar and H Olkowski, Common Sense Pest Control: Least toxic solutions for your home, garden, pets and community, Taunton Press, US, 1991.
1. K Snow, Mosquito nuisance and control in Britain: Results of new research, Environmental Health, October 1996.
2. Health & Safety Executive, New Biocidal Products Regulations Road Show Info Pack, February 2001.
3. C Swadener, Journal of Pesticide Reform, Vol 14 No.2, 1994.
4. M Craft, A Smell to Repel, BBC Wildlife Magazine, October 1996.
5. B Riley, Flyers Beware, Northwest Coalition for alternatives to Pesticides, US, December 1998.
7. The Pesticide Manual, British Crop Protection Council (BCPC), 2000.
8. The UK Pesticide Guide, BCPC, 2000.
[This article first appeared in Pesticides News No.51, March 2001, p20]