PLANT LICE. 165 
The genus Pemphigus is represented in our state by a num- 
ber of species, all producing peculiar galls. To give an idea of 
these insects the figures 144 to 146 are given. 
P, populi-transversus Ril. (The Poplar Gall-louse) makes a 
globular swelling on the petiole near the base of the leaf of the 
cottonwood (Fig. 144). The gall is formed by the folding or 
twisting of the petiole in such a manner that the edges come 
together and form a broad opening or mouth. 
P. vagabundus Walsh. (The Vagabund Gall-louse) causes 
irregular galls on the ends of twigs of poplars (Fig. 145). Such 
galls are not alone very unsightly, but they cause considerable in- 
oN 
Xp, 
Fic. 145—Pemphigus vagabundus Walsh. After Riley. 
jury to the tree, as the twigs stop growing at the ends. Such galls, 
green when young, but black later in the season, are very com- 
mon, and the only remedy we have to prevent the increase of 
the insects is to remove the galls while still green and to burn 
them. If we wait until they turn brown or black, which takes 
place in August, we simply remove the cradle of the lice, but not 
the lice themselves, as they have already left to spend the rest 
of their existence elsewhere. But where, is still an open ques- 
tion! 
P. fraximifolii Riley (The Ash-tree Plant-louse) is another 
louse, which curls the terminal leaves of the ash, forming a sort 
of gall. Where such lice abound the trees are greatly disfigured. 
