PLANT LICE
Heretofore, the species has remained on the apple trees, but now the winged ones are possessed with a desire for a change, a complete change both of scenery and of diet. They leave the apples, and when next discovered they are found to have established themselves in summer colonies on those common weeds known as plantains, and mostly on the narrow-leaved variety, the rib-grass, or English plantain (Fig. 99).
Fig. 99. The rosy apple aphis on narrow-leaved plantain in summer; above, a wingless summer form (enlarged)
As soon as the migrants land upon the plantains they give birth to offspring quite unlike themselves or any of the preceding generations. These individuals are of a yellowish-green color and nearly all of them are wingless (Fig. 99). So well do they disguise their species that entomologists were a long time in discovering their identity. Generations of wingless yellow females now follow upon the plantain. But a weed is no fit place for the storage of winter eggs, so, with the advent of fall, winged forms again appear in abundance, and these migrate back to the apples. The fall migrants, however, are of two varieties: one is simply a winged female like the earlier migrants that came to the plantain from the apple, but the other is a winged male (Fig. 100 A). Both forms go back to the apple trees, and
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