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. 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. Most insecticides are sprayed or dusted onto plants and other surfaces traversed or fed upon by insects. 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 synthetic insecticides penetrate by all three of these pathways, however, and hence are better distinguished from each other by their basic chemistry. 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). Insecticides can be classified in any of several ways, on the basis of their chemistry, their toxicological action, or their mode of penetration. Such substances are used primarily to control pests that infest cultivated plants or to eliminate disease-carrying insects in specific areas. Insecticide, any toxic substance that is used to kill insects. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.
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