|
About:
|
<a href="https://www.denentek.com/" target="_self">insecticide</a>, any toxic substance
that is used to kill insects. Such substances are used primarily to control pests that
infest cultivated plants or to eliminate disease-carrying insects in specific areas.
</p>
<p>
<br/>
</p>
<p>
Insecticides can be classified in any of several ways, on the basis of their chemistry,
their toxicological action, or their mode of penetration. In the latter scheme, they are
classified according to whether they take effect upon ingestion (stomach poisons),
inhalation (fumigants), or upon penetration of the body covering (contact poisons). Most
synthetic insecticides penetrate by all three of these pathways, however, and hence are
better distinguished from each other by their basic chemistry. Besides the synthetics, some
organic compounds occurring naturally in plants are useful insecticides, as are some
inorganic compounds; some of these are permitted in organic farming applications. Most
insecticides are sprayed or dusted onto plants and other surfaces traversed or fed upon by
insects.
</p>
<p>
<br/>
</p>
<p>
Modes of penetration
</p>
<p>
Stomach poisons are toxic only if ingested through the mouth and are most useful
against those insects that have biting or chewing mouth parts, such as caterpillars,
beetles, and grasshoppers. The chief stomach poisons are the arsenicals—e.g., Paris green
(copper acetoarsenite), lead arsenate, and calcium arsenate; and the fluorine compounds,
among them sodium fluoride and cryolite. They are applied as sprays or dusts onto the
leaves and stems of plants eaten by the target insects. Stomach poisons have gradually been
replaced by synthetic <a href="http://www.bapdapeng.com/technical-products/insecticide/"
target="_self">insecticide</a>s, which are less dangerous to humans and other mammals.
</p>
<p>
<br/>
</p>
<p>
Contact poisons penetrate the skin of the pest and are used against those arthropods,
such as aphids, that pierce the surface of a plant and suck out the juices. The contact
insecticides can be divided into two main groups: naturally occurring compounds and
synthetic organic ones. The naturally occurring contact insecticides include nicotine,
developed from tobacco; pyrethrum, obtained from flowers of Chrysanthemum cinerariaefolium
and Tanacetum coccineum; rotenone, from the roots of Derris species and related plants; and
oils, from petroleum. Though these compounds were originally derived mainly from plant
extracts, the toxic agents of some of them (e.g., pyrethrins) have been synthesized.
Natural insecticides are usually short-lived on plants and cannot provide protection
against prolonged invasions. Except for pyrethrum, they have largely been replaced by newer
synthetic organic insecticides as <a href="http://www.bapdapeng.com/technical-products/"
target="_self">technical products</a>.
</p>
<p>
<br/>
</p>
<p>
Fumigants are toxic compounds that enter the respiratory system of the insect through
its spiracles, or breathing openings. They include such chemicals as hydrogen cyanide,
naphthalene, nicotine, and methyl bromide and are used mainly for killing insect pests of
stored products or for fumigating nursery stock.
</p>
<p>
<br/>
</p>
<p>
Synthetic insecticides
</p>
<p>
The synthetic contact insecticides are now the primary agents of insect control. In
general they penetrate insects readily and are toxic to a wide range of species. The main
synthetic groups are the chlorinated hydrocarbons, organic phosphates (organophosphates),
and carbamates.
</p>
<p>
<br/>
</p>
<p>
Chlorinated hydrocarbons
</p>
<p>
The chlorinated hydrocarbons were developed beginning in the 1940s after the discovery
(1939) of the insecticidal properties of DDT. Other examples of this series are BHC,
lindane, Chlorobenzilate, methoxychlor, and the cyclodienes (which include aldrin,
dieldrin, chlordane, heptachlor, and endrin). Some of these compounds are quite stable and
have a long residual action; they are, therefore, particularly valuable where protection is
required for long periods. Their toxic action is not fully understood, but they are known
to disrupt the nervous system. A number of these insecticides have been banned for their
deleterious effects on the environment.
</p>
<p>
|