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Insecticides - cockroach treatments, flea treatments PDF Print E-mail

Some insecticides kill insects by being ingested and others kill on contact. Some work physically by abrading the waxy cuticle of insects so that they die from dehydration or they suffocate when their breathing pores (spiracles) are blocked by dust particles. Householders faced with an infestation of insects in the garden or house should choose a method of treatment that is least hazardous to themselves and the environment. Often, non-chemical methods such as traps, sticky bands around tree trunks or flywire screens can be used. Chemicals of low toxicity like borax or pyrethrum may also achieve the required result.

Synthetic insecticides such as the pyrethroids have low toxicity to mammals but are highly toxic to insects, and they do not decompose as rapidly as the natural product. Baits will limit spread of a chemical and are preferable to surface sprays. Synthetic chemicals such as organophosphates and carbamates kill the insects but are also toxic to humans and other animals to a greater or lesser degree.

Health effects
Synthetic insecticides have to be used with caution, particularly as most may be readily absorbed through the skin. Some are systemic in plants (they move through the whole plant) and cannot be removed from fruit or leaves by washing or peeling. Organochlorines are some of the most hazardous insecticides and have been widely used in the past, though they are now targeted for elimination and reduction under the 2001 Persistent Organic Pollutants Treaty (see Introduction). Their toxic effect on humans is often not immediately apparent, but they persist for years in the environment and accumulate in the fatty tissue of all living things. There is no animal now in the world which does not contain some DDT in its body, and the concentration increases up the food chain.

Organophosphates are another common type of insecticide. They do not persist as long in the environment as organochlorines, but they have high toxicity, are readily absorbed through the skin and chronic exposure may lead to long-term health effects.

Environmental effects
Some insecticides have been used so widely and frequently that the target insects have developed a genetic immunity to them. This is a danger with any insecticide which is used indiscriminately. Another problem is that useful as well as harmful insects may be killed. Bees are an obvious example of this; as well as producing honey they are essential for the pollination of many economically important crops.

A broad-spectrum insecticide will kill predatory insects which naturally control damaging insect populations. Such predators include lacewings, hover flies, some types of ladybirds and parasitic wasps which lay their eggs in caterpillars and aphids. Birds, which help to control insect populations, may also be killed by indiscriminate use of insecticides, particularly the organochlorines which also have been shown to act as endocrine disrupters (see Introduction).

Home owners use insecticides more intensively than do farmers and, therefore, each one of us is responsible for minimising their use and the adverse impact they have on the environment. This is particularly important in urban situations where houses and gardens are close together and an insecticide used in one house or garden can easily be blown into a neighbouring one.

Cultural controls, biological control and integrated pest management (see Introduction) offer alternative approaches which avoid many of the problems and hazards associated with many insecticides.

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