Plate XIX 



Fig. 1. Gall on Populus caused by Pempliigus oestlundi. (Cook, Rep. 

 Iiid. Dept. Gcol. and Nat. Res.) 



Fig. 2. Poplar Leaf Gall-louse, PempJiiyus popuUcauUs, and its gall: 

 a, incipient gall on under side of leaf; h, gall from the 

 upper side of the leaf ; e, mature gall, showing aperture ; d 

 and f, incipient double galls; /, wingless female; g, winged 

 insect — / and g enlarged as indicated. (Riley, Amer. Ent.) 



Fig. 3. Poplar transvei'se gall and louse, Pemphigus populi-fransver- 

 su.s: a, gall on Popidus leaf; h, gall showing aperture; c, 

 winged female louse; d, antenna of winged female. En- 

 larged as indicated. (Riley.) 



