158 TRANSACTIONS OF THE ILLINOIS 



the under side of the leaves with their colonies, and sometimes piled one 

 upon another. Dr. Fitch states that in 1855 the leaves of his cherry trees 

 were literally covered with these lice ; that at the time they were most 

 abundant he made an estimate of the number on a single small tree, but 

 ten feet high, and was astonished to find this to be at least twelve millions. 

 When very numerous, this species does not confine itself to the leaf 

 alone, but extends its colonies to the stalk, and even to the tender twigs 

 and buds and fruit stems, and occasionally to the green fruit. The tough^ 

 rigid texture of the cherry leaves prevents them from becoming wrinkled, 

 like those of some other trees ; but the margins curl, and there is a tend- 

 ency to curl backwards. When they attack very numerously the twigs 

 and young leaves, the extraction of the sap causes them to shrivel and die. 

 This species is quite common in Illinois, and, according to Walsh, has 

 been observed on the plum; but this fact appears somewhat at variance 

 with the fact that it will not develop on any species of the cherry except 

 the one mentioned. 



16. Aphis cerasicoleus, Fitch. Cherry-inhabiting Aphis. 



Pale greenish-yellow; antennae and legs, black; base of the thighs,, 

 pale ; nerves of the fore wings, dusky ; stigma, pellucid white ; honey- 

 tubes, quite short. When irritated, the legs and antennae emit from their 

 pores a bluish-white cotton-like secretion, which remains adhering to 

 them, and resembles fine mould. Length to the tip of the wings, 0.20. 

 of an inch. This is related to the preceding, and is found only on the 

 common black cherry. 



17. Aphis cerasifolice, Fitch. 



This is another species, described by the same author, which is found 

 on the under side of the leaves of the common choke-cherry. Its attacks 

 appear to be confined chiefly to the tender leaves at the ends of the twigs, 

 causing their margins to curl downwards and inwards, and changing their 

 color to a yellowish-green, the abdomen being coated with white powder, 

 except a line along the back and the sutures ; the legs and antennge are 

 dull white. 



The winged individuals measure about fifteen-hundredths of an inch to 

 the tip of the wings ; are black, with a pale green abdomen ; the latter 

 has three dark green dots on each side in advance of the honey-tubes, 

 and above these on each side a row of impressed deep green dots, and a 

 deep green stripe along the middle of the back ; the honey-tubes reach 

 half way to the tip of the abdomen and are dusky at the tips ; the antennje 

 are about two-thirds the length of the body, dusky or dull green at the 

 base ; beak, short ; legs, dull white; the feet and four hind femora (except 

 at base), blackish ; wings, pellucid; rib-vein, white; rest dark; second fork 

 very short. 



18. Aphis prunifolicB,Y\\.Qh. The Plum-leaf Plant-louse. 



This is much like the Apple-leaf Plant-louse, both in appearance and 

 habits, except that it selects the plum tree as its food plant instead of the 



