56 SOME INSECTS INJURIOUS TO TRUCK CROPS. 
number of them which happened to be in such locations. To deter- 
mine this point 80 beetles were placed in each of three lamp chimneys 
and set over clumps of grass. As the cool evenings approached the 
fleas worked down into the sod, and before the frost was off of the 
erass the next morning a heavy roller was run over these clumps 
from three different directions. The lantern chimneys were then re- 
placed and the sod taken into the laboratory. On examination only 2 
injured beetles were found. Twelve in the first clump, 10 in the sec- 
ond, and 15 in the third were uninjured. The other beetles were not 
recovered and probably escaped during the rolling. A large block in 
one of the yards was rolled over at this time (fig. 17), but no differ- 
ence could be seen between the number of beetles which emerged on 
the treated block and the number which came out on the rest of 
Fic. 17.—Rolling the hopyards with heavy roller, as an experiment in the control of the 
hop flea-beetle. (Original.) 
the field. The chitin of the hibernating beetles is very hard. The 
beetles are not readily injured when rolled between the thumb and 
finger, and it is very improbable that a satisfactory percentage could 
be killed by rolling the field in which the beetles are hibernating. 
SPRAYING. 
When the beetles became numerous on the sprouting hops, the pos- 
sibility of the use of contact insecticides or of arsenicals was brought 
to the attention of the writer, and a number of sprays were carefully 
tested. 
Blackleaf tobacco extract—Flea-beetles which were thoroughly 
drenched with blackleaf tobacco extract at the rate of 1 gallon to 65 
gallons of water soon died, but many beetles jumped through the 
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