Insecticide

An insecticide is a pesticide whose purpose is to kill or to prevent the multiplication of insects.

Insecticides are very widely used in agriculture, as well as in people's dwellings and workplaces. The use of insecticides is one of the major causal factors behind the increase in agricultural productivity in the 20th century.

Various plants have been used as folk insectides for centuries, including tobacco and pyrethrum.

Environmental Effects

One of the bigger drivers in the development of new insecticides has been the desire to replace toxic and irksome insecticides. It is interesting to note that the now notorious DDT was introduced as a safer alternative to the lead and arsenic compounds which had been used before. It is the case that when used under the correct conditions that almost any chemical substance is 'safe', but when used under the wrong conditions even the ' safest ' substance can be a threat to life, limb and/or the enviroment.

Some insecticides have been banned due to the fact that they are persistant toxins which have adverse effects on animals and/or humans. A classic example which is oftein quoted is that DDT is an example of a widely used (and maybe misused) pesticide. One of the better known impacts of DDT is to reduce the thickness of the egg shells on predatory birds. The shells sometimes become too thin to be viable, causing reductions in bird populations. This occurs with DDT and a number of related compounds due to the process of bioaccumulation, wherein the chemical, due to its stability and fat solubility, accumulates to progressively higher concentrations in the body fat of animals farther up the food chain. The near-worldwide ban on agricultural use of DDT and related chemicals has allowed some of these birds--such as the peregrine falcon--to recover in recent years.

On the other hand the thoroughly nasty longlived organochlorine Dieldrin if used with care can prevent termites from destroying the telephone cables, but it is clearly not suitable for aerial spraying to control insects in a field close to a school playground.

While the overuse of DDT lead to a reduction in its use, opponents of environmentalism often erroneously cite it as an example of environmentalism going too far and interfering with malaria eradication, going so far as to estimate the cost of human lives resulting from the DDT ban; for instance the novelist Michael Crichton states in his bestselling book, State of Fear:

"Since the ban, two million people a year have died unnecessarily from malaria, mostly children. The ban has caused more than fifty million needless deaths. Banning DDT killed more people than Hitler."

This accusation, while sensational, is erroneous, as no ban exists on the use of DDT for eradication of malaria or any other insect borne disease.[1] Groups fighting malaria have praised the ban on agricultural use of DDT, since it reduces the rate with which mosquitoes become resistant to DDT, which is the main reason it is not used more often to fight malaria:

"The outcome of the treaty is arguably better than the status quo going into the negotiations over two years ago. For the first time, there is now an insecticide which is restricted to vector control only, meaning that the selection of resistant mosquitoes will be slower than before." [2].

In fact, according to Agricultural production and malaria resurgence in Central America and India, Chapin, Georgeanne & Robert Wasserstrom, Nature, Vol. 293, 1981, page 183), the lives actually saved due to banning agricultural use of DDT can be estimated:

"Correlating the use of DDT in El Salvador with renewed malaria transmission, it can be estimated that at current rates each kilo of insecticide added to the environment will generate 105 new cases of malaria." It is interesting to note that Lindane and other insecticides have had to be used as an alternative to DDT becuase the population of insects have become resistant to DDT.

Some of the newer insecticides are more specific in their actions and are designed to break down into non-toxic components within a few days of application.

Application methods

Personal insecticide, commonly referred to as "bug spray", typically comes in a plastic bottle or aerosol can. Applied to clothing, arms, legs, and other extremities, the use of this pesticide will either ward off or kill nearby insects.

Insecticide used for killing pests—most often insects, and arachnids—primarily comes in an aerosol can, and is sprayed into the air or nest as a means of killing the animal. Fly sprays will kill house flies, blowflies, ants, cockroaches and other insects and also spiders.

Active ingredients of most bug sprays include permethrin and tetramethrin, which act on the nervous system of insects and arachnids.

Bug spray should be used in well ventilated areas only, as the chemicals contained in the aerosol and pesticide can be harmful or deadly to humans.

Individual insecticides

Chlorinated

Several are now banned because of their ecological persistence:

Organophosphorus

Chemically similar to Nerve agents

Plant toxin derived