Elementary entomology ([c1912]) Elementary entomology . elementaryentomo00sand Year: [c1912] 128 ELEMENTARY ENTOMOLOGY prove to be females, there usually being no males during the summer, and each gives birth to a similar number of young, the egg stage being passed within the body of the female and the young being born alive. Thus generation after gener- ation is produced, and a simple arithmetical cal- culation will show that the resulting progeny must soon become suf- ficiently numerous to entirely destroy the veg- etation from which the myriad little beaks are FIG. 175. Wingless female
Elementary entomology ([c1912]) Elementary entomology . elementaryentomo00sand Year: [c1912] 128 ELEMENTARY ENTOMOLOGY prove to be females, there usually being no males during the summer, and each gives birth to a similar number of young, the egg stage being passed within the body of the female and the young being born alive. Thus generation after gener- ation is produced, and a simple arithmetical cal- culation will show that the resulting progeny must soon become suf- ficiently numerous to entirely destroy the veg- etation from which the myriad little beaks are FIG. 175. Wingless female pea aphis and newly born young. (Enlarged) pumping out the sap. In the fall true males and females usually appear, and eggs are laid which hatch in the early spring. Most species are wingless until the food supply commences to get short, when the next gen- eration develops wings and migrates to new food plants. Many species have winged generations in the spring and fall, which —7 . i
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