39 Farmers’ Bulletin 1225. 
not be necessary if the first barrier is made at the edge of the field 
before any bugs have crossed the line and is maintained in an im- 
passable condition until migration has ceased. 
The barriers mentioned above are all dust barriers and are effective 
only when dry. In case of a shower a crust is formed on them over 
which the bugs can walk without hindrance, until the soil dries 
enough to allow redragging. As quickly-as the shower is over, oil 
or crude creosote may be poured in the groove of the groove-drag 
barrier or in the bottom of the trench barriers and in the groove of 
the ridge barrier. Very good results have been secured by throwing 
up a ridge, as indicated in method (4) above, and applying crude 
creosote in a line three-fourths of the way up the ridge instead of 
along its summit. Oil, to be effectual, must be kept soft in a con- 
tinuous line during every minute that the bugs are trying to cross the 
line. This requires several treatments during the first 24 hours, until 
the oil has made a hardened crust for itself, after which two treat- 
ments a day may be sufficient to keep the line continuously impass- 
able. An oil line in the floor of a trench barrier is very apt to become 
defective or passable from the falling of clods from the sides of the 
trench into the oil. 
Where special tools are not available smooth paths may be made 
along edges of a field by the use of a shovel, perhaps aided in places 
with a hoe or grubbing hoe, the path patted down with the back of 
the shovel, and an oil line laid on this path. The cost of labor with 
this type of barrier is likely to be much greater than with the other 
types. 
DESTROYING THE BUGS ALONG BARRIERS. 
As the bugs accumulate along the barriers some will be killed by 
the combined heat of sun and soil and suffocation by the dust. Large 
quantities can be killed by gasoline torches without disturbing the 
efficiency of the barriers, and burning as often as the massing of the 
bugs warrants is an effective way of destroying them. Another way 
to collect and destroy them is by digging holes at intervals of from 
15 to 30 feet with a post-hole auger on the bug side of the barrier, the 
edge of the hole touching the edge of the oi] line or the foot of the 
slope in the trench and ridge barriers. As the bugs come to a line 
which they can not cross they follow it and fall into the holes. If 
the holes are 12 to 18 inches deep, the bugs massing therein may die 
without further treatment. It is necessary, however, to watch that 
they do not climb out on trash blown into the holes. They may be 
killed by pouring a little coal oil into the holes, by burning, or merely 
by tamping. One difficulty with the postholes is that along the dust 
barriers they have to be remade with each renewal of the barrier. 
