FLIT manual spray pump for<unk> s from 1928 Farmer spraying an<unk>  on a cashewnut tree in Tanzania<unk> s are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively.<unk> s are used in agriculture, medicine, industry and by consumers.<unk> s are claimed to be a major factor behind the increase in the 20th-century's agricultural productivity. Nearly all<unk> s have the potential to significantly alter ecosystems; many are toxic to humans and/or animals; some become concentrated as they spread along the food chain.<unk> s can be classified into two major groups: systemic<unk> s, which have residual or long term activity; and contact<unk> s, which have no residual activity. The mode of action describes how the pesticide kills or inactivates a pest. It provides another way of classifying<unk> s. Mode of action can be important in understanding whether an<unk>  will be toxic to unrelated species, such as fish, birds and mammals.<unk> s may be repellent or non-repellent. Social insects such as ants cannot detect non-repellents and readily crawl through them. As they return to the nest they take<unk>  with them and transfer it to their nestmates. Over time, this eliminates all of the ants including the queen. This is slower than some other methods, but usually completely eradicates the ant colony.<unk> s are distinct from non-insecticidal repellents, which repel but do not kill.
Insecticide
Querulant
Toxicophore
Detergent
Corrosive substance
Deodorant
Antacid
Prebiotic 