Larvicides are toxic substances that act on insect larvae. To fight insects (see Disinsection ), larvicides and insecticides are used; the latter in one degree or another have larvicidal properties. Practically suitable only those larvicides (in the form of fine powders, solutions, emulsions on the surface), which do not dissolve or slightly dissolve in water. When using larvicides in the fight against the larvae of flies, preference is given to those larvicides that can be introduced into the substrate in a dissolved form. Insecticides can also be used. The oily substances that cover the reservoirs with a film also affect larvicides, which violates the respiration of insect larvae. The main means of fighting mosquitoes (including malarial), midges, biting midges and some other insects are larvicides that act when their larvae enter the intestine (intestinal larvicides); these include chlorinated hydrocarbons (DDT, hexachlorane, aldrin, dieldrin, etc.). However, due to cumulative properties, the use of DDT is currently strictly regulated. Among organophosphorus compounds, methyl nitrophos and baytex have the best larvicidal properties. All preparations of intestinal action (arsmal, Parisian greens, etc.) are slightly soluble in water and are used as larvicides in the fight against gnats.
Some larvicides quickly decompose ( organophosphorus compounds ), others retain their larvicidal properties for 1-5 years. In the fight against gnats, larvicides (DDT or hexachlorane dust) are used — 5–10 kg per 1 hectare of open area and 15 kg per 1 hectare of forest covered area. In the fight against flies, the sites of development of the larvae are treated; liquid wastes with a humidity of 70–80% are covered with a thin layer of larvicide (trichlorvos, chlorophos, karbofos, etc.); The film that is created leads to the fact that the larvae die when they rise to the surface of sewage.
People working with larvicides are provided with workwear and respiratory protection equipment; after work they must take a shower; wash hands and take off work clothes before eating.