Page:Insects - Their Ways and Means of Living.djvu/205

 LICE

Heretofore, the species has remained on the apple trees, but now the winged ones are possessed with a desire for a change, a cornplete change both of scenery and of diet. They leave the apples, and when next discovered they are found to have established thernselves in sumrner colonies on those cornmon weeds known as plantains, and mostly on the narrow-leaved variety, the rib-grass, or English plantain (Fig. 99)- As soon as the rni- grants 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 thern are wingless (Fig. 99)- So well do they disguise their species that ento- rnologists were a long tirne in discovering their identity. Generations of wingless vellow fernales now foll»w upon the plantain. But a weed is no fit place for the stor- age of winter eggs, so, with the advent of fall, winged forms again ap- pear In abundance, and F,ç. 99- The rosy apple aphis on nar- row-leaved plantain in summer; above, a these migrate back to the wingless summer form (enlarged) apples. The rail mi- grants, however, are of two varieties: one is sirnply a winged fernale like the earlier rnigrants that carne to the plantain from the apple, but the other is a winged rnale (Fig. 1oo A). Both forrns go back to the apple trees, and

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INSECTS