89 



and the irritation caused l)y them atlects the leaves as we have 

 seen. There is no regularity about the curling ; different leaves 

 curl diflbrenth , and those whicli I have seen here, as has been 

 noticed, curl more than is shown in figure (io. The curled leaf 

 affords shelter to the aphides^ and on opening it multitudes of 

 them may be found hidtlen witliin its folds, little grayish or black- 

 ish bodies. When" first hatched the lai-vie are light colored, but as 

 they grow older they grow darker ; the legs are always darker 

 than the body. According to Dr. Riley, the individuals of this 

 first generation complete their growth in about twelve days, though 

 the time varies with the season, for if cold days come the insects 

 are dormant for a time, and then development is retarded. There 

 are probably, Dr. Riley thinks, three molts. These, when mature, 

 are the " stem mothers," figure 65, b.^ and they live in the galls 

 which they have produced, and commence fdling the galls with 

 young, which are alive when produced, ami come at the rate of 

 " one every six or seven hours, according to temperature, increas- 

 ing in bulk and prolificacy from day to day, until by the early part 

 of May in the latitude of St. Louis, she has attained her fullest 

 development, and soon perishes. Riley, Bullet. United States 

 Geological Survey, Hayden, v, p. 5. 



The young of the second generation, those which come from the 

 offspring of the winter eggs, the "stem mothers " of Riley, are 

 very much like the parent, except that they never attain to so large 

 a size, and are rather different in color, being of a reddish brown, 

 or liver color. From these the third generation comes, and the 

 individuals of this generation differ considerably from the pre- 

 ceding. These latter are wingless, and are of the general form 

 shown in figure 05, b.^ while the third generation are like d. of 

 the same figure, and, as the figure shows, almost all the propor- 

 tions are changed. The wings do not appear at first, but are 

 developed as the insect becomes mature. Of these early genera- 

 tions Riley says : " During most of the month of May we may 

 find, where large clusters of leaves are affected, the few more or 

 less exhausted stem-mothers, and these second and third genera- 

 tions in every stage of development. As the lice increase in 

 number the leaves no longer protect them, but present on both 

 sides multitudes of busy atoms, livid old, and paler young, those 

 with wings and those getting wings, interspersed with white 

 exuviae, cottony secretion, and globules of pearly liquid. At the 



