89 
•PREVENTION AND REMEDY. 
The only preventive measure which I can suggest is based upon 
le probability that the plant-lice winter in the fields where they grow, 
rudence would consequently dictate that the kinds of plants attacked 
y them should not be raised upon the same ground two years suc- 
^ssively. It might suffice, however, to collect and burn the vines 
1 the fall. If the eggs are deposited upon them, this would an wer 
istead of a rotation of crops. The fact that the lice occur only on 
le lower surface of the leaves, which soon curl and wrinkle so as 
) protect them largely, made it very difficult to reach them with 
ay of the applications usually made to insects of this class. Ex- 
sriments were made, however, with substances in powder, with 
uids, and with vapors. 
The substances applied in powder were road dust and pyrethrum; 
le liquids were soapsuds and an emulsion of kerosene with milk: 
ad the vapors were tobacco smoke and vapor of bisulphide of 
irbon. 
In 
Several applications of dust were carefully made by hand to the 
ader side of the leaves. It did not adhere everywhere, but where 
did, the lice disappeared. As an average result, it was finally 
included that from One-third to one-fourth of the insects were killed 
: driven away by a single dusting. 
Powdered flowers of pyrethrum were dusted with the powder gun 
1 the under side of several leaves, which were thickly covered with 
,3e. These leaves were picked and placed in water for more careful 
i oservation. The powder was slow to act, not over five per cent, of 
le lice falling in an hour, but later nearly all fell. Most of these 
ere still alive on the table after tw r enty hours, but they finally all 
ed and dried up. Several other applications gave similar results. 
Strong soapsuds was sprinkled on the under side of other leaves 
lith little effect, although some of the lice were killed. 
An emulsion of kerosene was made as follows: one pint of hero¬ 
ine and two pints of milk were pumped back and forth with a 
cringe until a soft butter was formed, and this was diluted with 
n times its volume of water. Thrown upon the leaves with a 
7 ringe, this killed about all it reached, and cleared many leaves 
itirely, while on others a few remained. 
For the application of tobacco smoke, a common bee-smoker was 
fiained, filled with chunks of rotten wood mixed with cheap tobacco, 
jid fired as is usual in smoking bees. An immense smudge was 
Lsily made in this way, and kept under complete control. After 
•me successful experiments in the laboratory, the apparatus was 
l ken to the field. Merely to blow the smoke against the lice, without 
i*nfining it in any way, had no effect whatever. Large pieces of 
• /nvas (hay caps) were then obtained, and used to cover a section 
a row. Under these the tobacco smoke was blown repeatedly 
lie evening, keeping the space beneath well filled for the first five 
j inutes, and then for ten minutes. On examination next morning, 
>out ten per cent, of the lice were found dead as a consequence 
five minutes’ exposure, and from fifty to seventy-five per cent, of 
ose that had been exposed ten minutes. This experiment was 
