. Biology and human life. Biology. INSECTS IN RELATION TO HUMAN WEALTH 567 The botflies are repre- sentative of a large group of insects that are often injurious to horses and cattle (see Fig. 239). The ox warble lays its eggs on the cow. It is not certain whether the larvae work their way through the skin or from the alimentary canal. They finally lodge under the skin and thus ruin millions of dollars' worth of hides, besides making the animals sick and re- ducing their milk and beef values. 408. Fighting insects. One of the first sugges- tions that insects could be controlled by encour- agin
. Biology and human life. Biology. INSECTS IN RELATION TO HUMAN WEALTH 567 The botflies are repre- sentative of a large group of insects that are often injurious to horses and cattle (see Fig. 239). The ox warble lays its eggs on the cow. It is not certain whether the larvae work their way through the skin or from the alimentary canal. They finally lodge under the skin and thus ruin millions of dollars' worth of hides, besides making the animals sick and re- ducing their milk and beef values. 408. Fighting insects. One of the first sugges- tions that insects could be controlled by encour- aging other insects was made about a hundred years ago by two English entomologists, who de- clared that an increase in the number of ladybirds in greenhouses and fields. Fig. 236. dispar). The gypsy moth {Porthetria (a, b, c, slightly enlarged; d, slightly reduced) This animal was introduced into this country about 1869, in the course of some experiments made to find a substitute for the silk moth, and in twenty years it became so great a nuisance that the legislature of Massachusetts made an (ap- propriation for the study of methods to be used in checking the insect. In ten years over a mil- lion dollars was spent in the fight, but further work was stopped by some of the legislators whose regions had not been aft'ected. The insects then multiplied to such an alarming extent that in 1906 about a quarter of a million dollars was again spent in the fight, a, male adult; b, female; c, larva; d, pupa would clean out the aphids, or plant lice, and insure the hops against destruction (see Fig. 240). These predacious beetles do actu- ally devour vast numbers of soft-bodied scale insects and plant lice, which in turn live upon the juices of plants, sometimes causing the destruction of an entire Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectl
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