INSECTICIDE (from Lat. insectum, insect.
-cida, murderous, from re. to ]:ill). A substance used by mall to kill insects. Besides those materials properly included by this delini ti,n, however, there are many other agents of great, importance as insect exterminators. of \Odell the following may be classed as natural controls: Changes of temperature at critical times in the life histories of insects; rain, flood; drought ; forest and prairie tires; bacteria. fungi. mites, spiders, predaceous and parasitic insects, and other invertebrates; fish, reptiles, birds, ant eaters, and other vertebrates. Though of these exercises an important function in checking insect depredation. their offices are beyond scope of the present article, which deals With artificial or man-applied controls.
For convenience of discussion the elassitication of insecticides may be made according to the ways by which insects obtain foal. Plant feeding insects either chew plant tissue by means of movable jaws or else suck the juices through punctures in the epidermis manly by their tube-like beaks. The elbowing species may be subdivided into those that feed beneath the surface and those that feed in exposed positions. To the concealed feeders belong the leaf-miners, which live beneath the epidermis of leaves, etc.. and the borers in living and dead plants. timller, and grain. The only way these may be controlled are by poisonous gases (bean-weevil). by drown ing (peaeli-borers, sometimes), burning infested parts (raspberry cane-borer), or by digging them out (apple-borer), the feasible method deliending upon the habit of the species. To the exposed feeders belong caterpillars. grasshoppers. beetles, etc., which are usually controlled by intestinal poisons, such as arsenical compounds. especially Paris green used at the rate of a pound in front 100 to 300 gallons of water, Bordeaux mixture. (See FuNniciDE.) Another popular poison is arsenate of lead, which adheres to the foliage better than Paris green, and may be applied in larger quantities with less danger of injury. Of the newer insecticides, green arsenoid is con sidered valuable. 11ellebore is most frequently used upon small plants, especially for the cur rant-worm. lt is also sprayed upon fruits ap
proaching maturity. Some soft-bodied insects may Ice controlled in the same way as sucking insect s.
Sucking insects. among which are some of the most destructive pests of crops, cannot be con trolled by stomach poisons, because they obtain their food from beneath the epidermis of the plant. Because cif their small size. insidious habits, enormous prolificacy, or capability of withstanding treatment, they are among the most dreaded crop pests. Some (e.g. the squash-bug) have never been effectually and economically controlled by any method yet devised. In general the most feasible controls are slieh as either obstruct the passages of the insects (tobacco and insect powder), or have a caustic action upon their skins (kerosene and whale-oil soap). Since kerosene can rarely be applied xvith safety to growing plants, it is emulsified by and churning violently two gallons of kerosene with a solution of eight ounces of hard soap in one gallon of hot water, and diluted when needed for use with from five to ten times as much water. Experiments have been made with pumps that mix kerosene and water in 'definite proportions as they are drawn from two respective tanks by the one piston-stroke. If successful, such pumps will save much dis agreeable W reeable labor. hale-oil soap is applied as a solution of one pound in one to ten gallons of water. Certain inserts, notably the San dosili scale, a serious pest of woody plants, and the chinch-bug, an equally troublesome pest of -cereals. have been experimented upon in a unique way; diseases were spread among them, in the first case by means of infected water sprayed them; in the latter by infected insects. Results were not particularly satisfactory in either ease. Not so in the case of the cottony cushion scale, a pest on citrus trees in California. A ladybird beetle, imported from Australia, in a few years extirpated the pest. This is perhaps the most notable instance of luau's utilizing a natural control and making it an insecticide in the narrow sense. See LADYBIRD.