In more recent years lime-sulphur combina tions have been used as washes and sprays against scales and other sucking insects with good results. Still more recently nicotine sul phate standardized at 40 per cent purity has come into general use as a contact insecticide for the same class of insects, and is now a standard remedy in combination with soap for the control of aphides or plant-lice, the onOn and pear thrips and related species, leafhoppers, plant-bugs and many others. Prior to this time tobacco preparations were used but with in different success except on a restricted number of insect pests.
Quassiin is the subject of investigation as a contact insecticide. Of arsenical poisons arse nite of zinc and arsenate of calcium are effec tive but not superior to arsenate of lead. Ad hesives, such as whale-oil (fish-oil) and other soaps, are also in general use under the name of ((stickers.° Repellents, to prevent such in sects as the parent flies of root-maggots from depositing their eggs, are being successfully em ployed and in some cases odorous substances are being used to attract insects from their nat ural foods where they can be destroyed.
As fumigants, hydrocyanic-acid gas gener ated from sodium cyanid is in general use for the destruction of mill and granary insects, greenhouse and household pests. Carbon te trachloride and para-dichlorobenzene are excel lent fumigants, but too costly for general use. Insects affecting stored products and pests in households may also be controlled by heat — an old remedy which is now employed in many mills and warehouses where steam-heating plants are installed.
During the early years of work in spraying for various insects the principal dependence was placed in American insecticide machinery, but after the invention of different forms of nozzles by M. Vermorel, of France, various other noz zles, pumps and other machinery were invented in America and have gone into general use.
An almost incredible number of spraying machines and appliances are being manufactured and constant improvements are being made adapted to special purposes.
Prevention of Insect Injuries by Farming would be difficult to detail step by step the wonderful progress that has been made in means of subduing insects by simple farming methods which, as a rule, neces sitate little or no extra labor or monetary (nit lay. Some of our principal pests, with which we cannot cope successfully by means of in secticides or by mechanical methods, may be controlled by the judicious use of ordinary methods of tillage. The seed, nursery or other stock for planting should be selected with a special view to securing immunity from attack by the insect most feared or most prevalent in tfie region where the crop is to be planted. By planting different immune varieties of wheat the ravages of the Hessian fly are reduced to a minimum. Certain forms of trees may be selected for planting for shade in some regions without danger of injury, because the insects which elsewhere do greatest damage to them are not present. The selection of a suitable location on the farm for a crop should be made with the same end in view. Where injury is feared by an insect which does not travel freely, immunity can be secured by planting in that part of .the farm where the insect is known not to exist. The prompt destruction of crop rem nants and the pulling up and burning over of weeds and other rubbish is a preientive ap plicable to all crops. Another measure is the use of °trap crops.° Thus part of an old crop may be left to attract insects which usually remain in the field after the crop is made; similar or more attractive plants may be grown for the protection of the main crop; or of early vaneties of the same plants, as lures for the insects until the main crop can obtain a good start. On the lure plants the congregated
insects must be destroyed by poisons or by fire. Trap crops are of considerable value in the treatment of several of the worst enemies of cucumbers, melons, squashes and similar vines. The stimulation of a plant by means of fertili zers and the maintenance of healthy, vigorous growth by cultivation, the suppression of dis eases and the prevention of injury by insect pests other than those which it is specially designed to circumvent, are helpful aids. Crop rotation or the planting of alternate crops which are not injured by those insects which ravage the staples assists in the warfare; as also do fall and spring plowing, which, in proper combination, result in the destruction of nearly all forms of the many insects which pass one or more stages in the earth in hibernation. The use of water by irrigation or submersion, if practised at the right time, will result in the temporary extirpation of nearly all insects in the fields thus treated, particularly in cranberry bogs. The reclamation by drainage of land subject to more or less complete submersion, such as swampy tracts, river bottoms and the like, and the destruction of the weeds and other plants and the insect life which remain by burning over, are of great value in suppressing many pests. If, to the methods above out lined, we add the strict observance of timely harvesting of crops with a view to the preven tion of further attack and the destruction of insects which might reproduce the following year; the utilization of natural enemies, such as parasitic and predaceous insects, poultry and live stock, to destroy the insects in the field after the crop is off ; the systematic inspection of the farm for the first appearance of insect attack, and, finally, the co-operation of neigh boring farmers having a community of inter ests in growing the same crops, there is com paratively little use for insecticides save in the case of insects such as grasshoppers and the caterpillars of moths and butterflies, which are strong fliers and cannot be successfully con trolled by mechanical methods.
Econom1/4
Dr. T. W. Har ris is creffited with having been the first eco nomic entomologist of America, but in realny , the honor is due to W. D. Peck, who beean writing on injurious insects late in the 18th century (1795-1819). His writings, however, are few, in comparison to those of Harns, whose labors began in 1831 and whose greatest work appeared in 1841, his classic treatise on
When Dr. Riley assumed the duties of ento mologist of the United States Department of Agriculture, economic entomology received a new impetus, his work and that of his assist ants marking a new era in practical entomologi cal work Upon his death in 1894, he was succeeded by Dr. L. 0. Howard, under whose direction the Bureau of Entomology continues to issue reports, bulletins and circulars of the highest practical and scientific value. See