89 
PREVENTION AND REMEDY. 
The only preventive measure which I can suggest is based upon 
the probability that the plant-lice winter in the fields where they grow. 
Prudence would consequently dictate that the kinds of plants attacked 
by them should not be raised upon the same ground two years suc- 
cessively. It might suffice, however, to collect and burn the vines 
in the fall. If the eggs are deposited upon them, this would answer 
instead of a rotation of crops. The fact that the lice occur only on 
the lower surface of the leaves, which soon curl and wrinkle so as 
to protect them largely, made it very difficult to reach them with 
any of the applications usually made to insects of this class. Ex- 
periments were made, however, with substances in powder, with 
fluids, and with vapors. 
The substances applied in powder were road dust and pyrethrum ; 
the liquids were soapsuds and an emulsion of kerosene with milk: 
and the vapors were tobacco smoke and vapor of bisulphide of 
carbon. 
Several applications of dust were carefully made by hand to the 
under side of the leaves. It did not adhere everywhere, but where 
it did, the lice disappeared. As an average result, it was finally 
concluded that from one-third to one-fourth of the insects were killed 
or driven away by a single dusting. 
Powdered flowers of pyrethrum were dusted with the powder gun 
on the under side of several leaves, which were thickly covered with 
lice. These leaves were picked and placed in water for more careful 
observation. The powder was slow to act, not over five per cent. of 
the lice falling in an hour, but later nearly all fell. Most of these 
were still alive on the table after twenty hours, but they finally all 
died and dried up. Several other applications gave similar results. 
Strong soapsuds was sprinkled on the under side of other leaves 
with little effect, although some of the lice were killed. 
An emulsion of kerosene was made as follows: one pint of kero- 
sene and two pints of milk were pumped back and forth with a 
syringe until a soft butter was formed, and this was diluted with 
ten times its volume of water. Thrown upon the leaves with a 
syringe, this killed about all it reached, and cleared many leaves 
entirely, while on others a few remained. 
For the application of tobacco smoke, a common bee-smoker was 
obtained, filled with chunks of rotten wood mixed with cheap tobacco, 
and fired as is usual in smoking bees. An immense smudge was 
easily made in this way, and kept under complete control. After 
some successful experiments in the laboratory, the apparatus was 
taken to the field. Merely to blow the smoke against the lice, without 
confining it in any way, had no effect whatever. Large pieces of 
canvas (hay caps) were then obtained, and used to cover a section 
of a row. Under these the tobacco smoke was blown repeatedly 
one evening, keeping the space beneath well filled for the first five 
minutes, and then for ten minutes. On examination next morning, 
about ten per cent. of the lice were found dead as a consequence 
of five minutes’ exposure, and from fifty to seventy-five per cent. of 
those that had been exposed ten minutes. This experiment was 
