168 TRANSACTIONS OF THE ILLINOIS 





Aphis humuli, Schrank. The Hop Plant-louse. 



This species is probably identical with the Hop Aphis of Europe, and 

 does more injury to the plant it attacks than is done by any other aphis to 

 the plants which they infest. They are found on the under side of the 

 leaves of the hop, often in immense numbers; they sometimes cover the 

 upper surface of the leaves with their honey-dew to such an extent that it 

 afterwards changes to a sooty black, giving rise to what is called " black 

 blight." 



The young lice are of a yellowish-white color, with black eyes, but 

 as they increase in age and size they change to green. The winged indi- 

 viduals are green, with the back of the thorax and the breast black ; the 

 abdomen has a row of black dots each side, and some transverse black 

 bands ; legs, yellowish, except the feet and joints, which are black. The 

 antennae nearly as long as the body, black, except at the base ; honey-tubes 

 rather long, and dusky at the tips ; wings transparent, with the stigma 

 greenish-gray, and veins brownish. 



34. Aphis rudbeckicE, Fitch. 



Is a large, red plant-louse, which often congregates in immense num- 

 bers, head downwards, on the stalks of the Golden-rod, and appears to be 

 a different species from A. soiidaginis, Hausm., which infests the stems 

 of the European Golden-rod {So/idago virgaiired). Red ; antennce and 

 legs black, basal half of the thighs yellow ; honey-tubes equaling the 

 length of the tip of the abdomen ; stigma of the fore wings, yellowish ; 

 veins, brown ; the marginal or costal one, sulphur-yellow. Length, 0.20 

 of an inch. It also infests Rudbeckia laciniata. 



15. Aphis {Siphonophord) lactucce, Linn. The Lettuce Plant-louse. 



There are more than one species of plant-louse found on the common 

 garden lettuce {Lactuca oleracea), but the others, or rather the other 

 species is easily distinguished from this, as it belongs to the Woolly Aphis 

 group and operates chiefly on the roots, while this operates on the leaves 

 and belongs to the typical species of Aphis, which has caused Koch to 

 remove it to the genus indicated. I take it for granted that our species 

 is identical with the European species. It is very variable in its mark- 

 ings, hence we are led to rely chiefly upon habits in determining it. I 

 give here a description of some of the varieties of the European species, 

 that the readers may have the means of comparison. 



The Viviparous Winged Female. — Grass-green ; head and chest, black 

 above and below ; front and hind border of the prothorax, green ; a row 

 of black spots on each side of the abdomen ; antennae, black, a little 

 longer than the body; beak, pale yellow, with a black tip; honey-tubes 

 about one-fourth the length of the body, black ; legs, pale yellow, rather 

 long; feet and tips of the thighs, black; wings, transparent, much longer 

 than the body ; rib-vein, yellow ; branch veins, brown. 



There is also a smaller gray variety, with the fore chest pale red, 

 middle chest black, and honey-tubes yellow. 



