4 
These multiply with astonishing rapidity * for from five to twelve 
generations, carrying us in point of time to the hop-picking season. 
Fic. 3.—The Hop Plant louse, third generation on Plum—the generation which flies to the hop— 
enlarged; head below at right—still more enlarged. 
There then develops a generation of winged females which fly back to 
the plum tree and give birth to the true sexual females (Fig. 4), which 
never acquire wings and never leave the plum 
tree. By the time this generation has matured, 
which involves but a few days, varying according 
to the temperature, belated winged individuals, 
which are the true males (Fig. 5), fly in from the 
hop fields. These fertilize the wingless true 
females upon the plum leaves and these soon 
thereafter lay the winter-eggs. Thus there is but 
one generation of sexed individuals produced 
and this at the close of the life-round—the fe- 
males wingless on plum trees; the males winged 
a ( on hops. All intervening generations are com- 
Fic. 4.—The Hop Plant-louse, posed of virgin females only (parthenogenetic). 
true, sexual fema]e—en- ng Fi > S = 
larged. This is the invariable round of the insect’s life. 
> 
¥ ) S) 
2 REMEDIES. 
From the life history just given three important facts are obtained : 
(1) It will pay to nakea preventive application of some one of the mix- 
tures mentioned further on, with apparatus there described, to all plum 
trees in the neighborhood of hop yards, either (@) in the spring before 
* Each female is capable of producing on an average about one hundred young, at 
the rate of three per day under favorable conditions. Each generation begins to 
breed about the eighth day after birth, so that the issue from a single individual runs 
up, in the course of asummer, to trillions. The issue from a single stem-mother may 
thus, under favorable conditions, blight hundreds of acres in the course of 2 or 3 
months. 
