204. : PLANT LICE. 
Fig. 163. Somewhat later true males appear on the hop, Fig. 
164. Seeking the females on the plum, they pair very late in 
the season with the wingless true females, who deposit their 
eggs as already mentioned, Fig. 165. As many as twelve gen- 
erations of the lice can be produced in a single season, and when 
we consider that “each parthenogenetic female is capable of pro- 
ducing on an average one hundred young, (the stem mother 
probably being more prolific), at the rate of one. to six, or on 
an average of three per day, under favorable conditions” (Riley),. 
we can well realize how much injury can be caused by plant-lice, 
for all suck the liquid sap from the plants they infest. 
Hop growers, to prevent losses from these lice, should not 
permit any wild or cultivated plum trees to grow near their hop. . 
yards; a very simple remedy, providing they have no slovenly 
neighbors. 
Fic. 163—Phorodon humuli Schrank.—True sexual female, enlarged. After Inscct- 
Life, Div. of Entomology, Dep. of Agriculture. 
Remedies against Plant-lice. 
In some cases remedies have already been suggested. It 
is of course impossible to lay down general rules as to the treat- 
ment of all plant-lice, since their habits differ so greatly, but 
there are a few points that should be known. 
The earlier the plant-lice are dealt with the better is the 
chance to eradicate them, hence remedies should be applied as. 
soon as the lice are noticed. If we wait they increase rapidly and. 
the plants at the same time -become weaker and less resistant. 
