Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 422 ELEMENTARY BIOLOGY 450. Fighting insects. One of the first suggestions that insects could be controlled by encouraging other insects was made about a hundred years ago by two English entomologists, who declared that an increase in the number of ladybirds in greenhouses and fields would clean out the aphids, or plant lice, and insure the hops against destruction (see Fig. 224). In this country various species of native ladybirds serve as effec- tive checks upo
Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 422 ELEMENTARY BIOLOGY 450. Fighting insects. One of the first suggestions that insects could be controlled by encouraging other insects was made about a hundred years ago by two English entomologists, who declared that an increase in the number of ladybirds in greenhouses and fields would clean out the aphids, or plant lice, and insure the hops against destruction (see Fig. 224). In this country various species of native ladybirds serve as effec- tive checks upon plant lice of many kinds. It has been possible to control the destructive Hessian fly by means of the parasite Polygnotus.
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