THE ALFALFA CATERPILLAR. 13 
be saved, but the major portion of the larve, finding a lack of the 
food necessary for their complete development, will ultimately perish. 
To bring about this condition, however, it is necessary to mow the 
field carefully, leaving no high stubble. The turnrows, borders, 
and ditch banks should also be closely mown, as this will not only 
reduce the supply of food for the larve but also that of the butter- 
flies, as such plants will afford considerable bloom. In two cases in 
the writer’s experiments it became necessary to remow the fields 
at a cost of from 30 to 50 cents per acre, and then in all cases to 
irrigate promptly. As a result of this procedure a large percentage 
of the caterpillars failed to develop to the imago or butterfly stage. 
Deducting these, together with the larger number that failed to 
reach the pupal stage, it will be seen that there were many hundred 
less worms to attack the next crop, as each butterfly developing from 
them would have deposited at least 100 eggs. In some fields, in- 
stead of irrigating immediately after the hay was removed, the 
experiment was tried of letting the field go dry for several days, 
and thus starving the worms. While this gave good results it was 
not as satisfactory as the method of immediate irrigation, for there 
was always enough moisture in the field to start the new crop going 
and thus provide a little food for the caterpillars. 
The complete success of these methods is dependent on cooperation 
among the farmers, for the larger the percentage of those who in- 
augurate a good cultural system the greater will be the benefit derived 
therefrom. The butterflies, however, do not fly very long distances, 
and as long as the conditions are favorable for their existence on one 
field or on one ranch they will remain there. They may, however, 
fly considerable distances when forced to do so for want of food or 
for fresh green alfalfa on which to deposit eggs or when driven by 
the wind, and thus it is that one farmer can secure, by his individual 
efforts, such remarkable results as are reported below. 
RESULTS OBTAINED. 
Of the ten fields cultivated according to these methods only one was 
damaged by the caterpillars up to July 10, the date on which so large 
a number of them were killed by the disease previously mentioned. 
This one field was damaged because irrigation had been delayed for 
nearly two weeks after the cutting of the second crop, owing to a new 
ditch which was under construction. Being a thrifty field naturally, 
the alfalfa had made a start, assisted by the moisture still present in 
the ground, and butterflies coming in from an outside field deposited 
eggs on this new growth, thus enabling the worms to destroy the best 
of the crop after it was finally irrigated. As a result almost an en- 
tire crop was lost. A field adjoining on the south, which had been 
[Cir. 133] 
