Everything about Insecticides totally explained
An
insecticide is a
pesticide used against
insects in all developmental forms. They include ovicides and
larvicides used against the
eggs and
larvae of insects respectively. Insecticides are used in
agriculture,
medicine,
industry and the
household. The use of insecticides is believed to be one of the major factors behind the increase in agricultural productivity in the 20th century. Nearly all insecticides have the potential to significantly alter ecosystems; many are toxic to humans; and others are concentrated in the food chain. It is necessary to balance agricultural needs with environmental and health issues when using insecticides.
Classes of agricultural insecticides
The classification of insecticides is done in several different ways:
- Systemic insecticides are incorporated by treated plants. Insects ingest the insecticide while feeding on the plants.
- Contact insecticides are toxic to insects brought into direct contact. Efficacy is often related to the quality of pesticide application, with small droplets (such as aerosols) often improving performance.
- Natural insecticides, such as nicotine and pyrethrum, are made by plants as defences against insects. Nicotine based insecticides have been barred in the U.S. since 2001 to prevent residues from contaminating foods. (External Link
)
- Inorganic insecticides are manufactured with metals and include arsenates copper- and fluorine compounds, which are now seldom used, and sulfur, which is commonly used.
- Organic insecticides are synthetic chemicals which comprise the largest numbers of pesticides available for use today.
- Mode of action -- how the pesticide kills or inactivates a pest -- is another way of classifying insecticides. Mode of action is important in predicting whether an insecticide will be toxic to unrelated species such as fish, birds and mammals.
Heavy metals, for example
lead,
mercury,
arsenic, as well as plant toxins such as
nicotine have been used for many years. Various plants have been used as folk insecticides for centuries, including
tobacco and
pyrethrum. Some farmers are reporting successfully using spray of crudely fermented alcohol as an effective insecticide.
Organochlorides
With the rise of the modern chemical industry it was possible to form
organochlorides, such as
chlorinated hydrocarbons. The organochlorides used in chemical warfare tend to be more potent
electrophiles than those used as insecticides. For instance
mustard gas (
sulfur mustard, HD) is a potent alklating agent which uses
neighbouring group participation of the sulfur to make the
alkyl chloride a stronger electrophile. It is likely that the chlorine in DDT is used to tune the
lipophilicity of the compound, and to alter the shape and electrostatic effects involved in the interactions of the insecticide and the biomolecules in the target organism. For instance DDT works by opening the
sodium channels in the nerve cells of the insect.
Organophosphates
The next large class was the
organophosphates, both the insecticides and the chemical warfare agents (such as
sarin,
tabun,
soman and
VX) work in the same way. All these compounds bind to acetylcholinesterase and other cholinesterases. This results in disruption of nervous impulses, killing the insect or interfering with its ability to carry on normal functions.
Carbamate insecticides have similar toxic mechanisms but have a much shorter duration of action and are thus somewhat less toxic.
Organophosphates have an additive toxic effect to wildlife, so multiple exposures to the chemicals amplifies the toxicity.
Sprayed insecticides may drift from the area to which it's applied and into wildlife areas, especially when it's sprayed aerially. in which worker bees from a
beehive or
Western honey bee colony abruptly disappear. Loss of pollinators will mean a reduction in crop yields. (bug found in stored cereal)
Polyketide
Pyrethrum
Quassia
TetranortriterpenoidFurther Information
Get more info on 'Insecticides'.
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