MEANS OF CONTROLLING INSECTS Careful estimates indicate that the value of farm products now destroyed each year by insects in the United States aggregates the vast sum of $700,000,000, or more than the entire expenditures of the national government. Thus, one of the most serious problems that confront the American agri culturist is that of controlling the insect enemies of his crops. He is now menaced by nearly twice as many different kinds of insect pests as in 1850, and three or four times as many as a century ago. And the outlook is far from encouraging, for all the old pests will doubtless continue their ravages indefinitely, with "up" and "down" periods at un certain intervals. Furthermore, the American agriculturist will have the best plants and animals the world produces, no matter whether he does thereby introduce other such destructive pests as the San Jose scale from China. There are still many insect pests in Europe, Asia, Australia, Africa and Mexico that are liable to be introduced at any time, and they may be much more destructive here than in their native home, where their enemies and surrounding conditions largely hold them in check. Thus, the unbroken ranks of the insect pests of a century ago will be constantly augmented by new kinds that are either disturbed by man in their wild haunts here (as the Colorado potato-beetle), or that come in naturally from adjoining countries (as the cotton boll-weevil from Mexico), or that are brought in by commerce from foreign lands (as the cattle horn-fly and over half of the other standard insect pests).
But the outlook is not really so gloomy, for the American agriculturists are well equipped with insecticidal batteries, and they are waging a most scientific and successful fight against in sect enemies. Many millions of dollars are being spent annually in America by national and state governments and by individuals in fighting insects and in devising and testing new remedial meas ures; it is estimated that over $8,000,000 is expended each year in spraying apple trees for the codling-moth alone.
Natural checks.
In this warfare that man must wage against his insect foes, he should not forget that nature has provided active and often very effective insect destroyers without which man could not grow crops, or even exist himself. Were it not for the
many little enemies of plant-lice, these insignificant creatures with their wonderful powers of multipli cation would soon overrun the earth, and destroy all vegetation, thus robbing man of his primary food supply. Among the forces of nature which thus aid man in his insect warfare may be men tioned strong winds, sudden changes of tempera ture in winter, rains, and forest and prairie fires. Then among the plants and animals there are some very efficient insect-destroyers. Bacteria and fungi often kill a large proportion of army-worms or chinch-bugs that are devastating crops. Many of the birds feed largely on insects and should be encouraged to stay on every farm, for they are among the most effective of nature's insect-des troyers.
But it is among their own kind, the insects, that insect pests find their most destructive foes. Vast numbers of insects, some so tiny that several of them can live inside an insect egg (codling-moth egg) not larger than a pin's head, are constantly prey ing on the insect enemies of man's crops. And these parasitic and predaceous insects are often very effective in aiding man in his strenuous war fare to protect his crops from insect pests. A little lady-bird beetle saved the citrons industry of Cali fornia from destruction by a scale insect, and it would be impossible to grow wheat successfully in many sections of the United States were it not for the tiny insect parasites of the hessian fly.
Man is coming to realize more and more the value of these natural aids in his warfare against insect pests. In Hawaii and California, thousands of dollars are expended annually in searching for and importing from foreign lands beneficial insects to prey on insect pests, and some striking successes have been attained. Europe is now being searched for the natural enemies of the gypsy and brown tail moths to aid in checking and finally controlling these serious pests.