PLANT LICE. 189 
pearance and the equally sudden re-appearance at somewhat fixed 
intervals, of these pests. This peculiarity is usually accounted 
for by the condition of the weather. In England it is supposed 
to be caused by an east wind, and is called ‘Blight.’ The truth 
of the matter is that some of these pests have fixed habits of 
migrating and are not dependent on the conditions of the weather. 
In order that florists, horticulturists and agriculturists may better 
be able to take preventive measures against their rapid increase, 
it is well to know where to find them at all seasons of the year. 
At times when they are all supposed to be dead, destroyed by 
the weather or some other dispensation of Providence, they may 
be increasing in destructive numbers on some useless plant in a 
neglected corner. 
“Though it has long been surmised by entomologists that 
many of the species of plant-lice migrate from one kind of plant 
to another, during part of the season, but few species have been 
proven to have this habit. The Snowball and Waahoo Louse 
both have this habit of migrating. The history of the Waahoo 
Louse is as follows The eggs which are deposited around the 
buds of Waahoo (Euonymus atropurpureus) hatch between the 
middle of April and the first of May. All of the brood from the 
ege are wingless. After moulting two or three times each in- 
dividual, all being females, begin to deposit young plant-lice like 
themselves on the under side of the leaves, which the stem- 
mothers have caused to curl slightly. When full grown the 
second brood develop wings, and migrate to such weeds as 
Shepherd’s Purse, Curled Dock, Pigweed, and Thistle. This mi- 
gration occurs between May 2oth and June roth. They remain 
on these weeds throughout the summer. The number of broods 
produced during the summer is not known. In this locality they 
seem to prefer the Pigweed (Chenopodium album). Feeding as 
they do on the flower spikes, they resemble the seeds of the weeds 
and are easily overlooked. 
“The latter part of August another brood of winged females 
appear on the Pigweed. These migrate back to the Waahoo on 
the leaves of which a wingless brood is deposited. This wingless 
brood is the last of the season. About the time the latter are 
deposited on the Waahoo, a brood of males are deposited on the 
pigweed, which develop wings, migrate to the Waahoo, and pair 
