7J 



116 THE STUDY OF INSECTS 



the fall on a certain plant which is called the primary host plant; but in 

 the spring when the stem-mothers have appeared and have given rise to 

 winged forms in the second and third generations these winged aphids 

 become migrants and fly to another perhaps totally unrelated plant, 

 which is called the secondary host plant. On this plant the aphids live 

 during the summer but return to the primary host plants in the fall on 

 which the sexes are produced and the eggs are laid. 



The potato aphid, Illinoia solanifolii, deposits its eggs in the fall on 

 the rose, its primary host plant; but in the spring the winged migrants 

 leave the rose and go to the potato to pass the summer. Toward fall 

 winged forms appear and return to the rose where the sexual forms are 

 produced and the eggs are laid. 



The rosy apple aphid, Anuraphis roseus, is another example of this 

 habit. The eggs of this aphid are deposited on the apple in the fall but 

 in the spring winged migrants fly to the narrow-leaved and broad-leaved 

 plantains and on these plants the insects pass the summer. 



Some aphids are bark-feeding. For example, the giant hickory aphid, 

 Longistigma carycz, is found feeding on the branches of hickory, maple, 

 and other forest trees. It is the largest aphid known, 

 measuring nearly ^ of an inch to the tips of its wings (Fig. 

 194). 



Other aphids are leaf-feeding like the potato aphid al- 

 fig 194. — The ready mentioned and the spring grain aphid, or "green 



Kiant hickory aphid. 1 ,, ^ „ .. „ 1 • 1 • • • • j. 1 



bug, 1 oxoptcra graminum, which is so injurious to wheat 

 and oats in some seasons in the Mississippi Valley. 



There are also root-feeding species. For instance the corn-root aphid, 

 Anuraphis maidiradicis, which is such a pest on the roots of corn in the 

 Mississippi Valley; and the strawberry-root aphid, Aphis forbesi, which 

 infests the roots of strawberry plants. Both of these species are attended 

 by ants and placed upon the roots of corn and strawberries by the ants. 



Some aphids secrete great quantities of white waxy threads which 

 cover their bodies like wool. These are known as the woolly aphids. 

 One of these woolly aphids which occurs on the apple, is known as the 

 woolly apple aphid, Eriosoma lamgera. It has a complex life history. 

 Its eggs are deposited on the bark of the elm. There they hatch in the 

 spring and the young crawl to the leaves and by their presence produce 

 rosettes at the ends of branches. Later, winged forms go to the apple 

 where several generations are produced, some of which live on the 

 branches and some on the roots underground. The root form may be 

 very injurious to the trees, especially in sandy soil. Finally in the autumn, 

 the winged forms on the apple fly back to the elm where the sexual 

 individuals are produced and the eggs are laid. It should be said that 

 some of the aphids remain on the apple trees all winter. 



Large numbers of a woolly aphid are often found crowded together on 

 the under side of the branches of alder. This species is known as the 

 alder-blight, Prociphilus tessellata. In addition to the white excretion 

 with which the body is covered this insect excretes large quantities of 

 honey-dew. The result is that the branches infested by this insect, and 

 those beneath the clusters of aphids, become blackened with fungi that 

 grow upon this secretion. There is also a curious fungus which grows in 

 large spongy masses beneath the clusters of plant-lice; this is known as 

 Scorias spongiosa. It grows in the honey-dew that falls upon it. 



