30 BULLETIN 124, IT. S. DEPARTMENT OF AGRICULTURE. 
flies to feed upon and to the fact that the greater part of the fields 
was kept closely grazed, making the alfalfa less favorable for the 
laying and development of the eggs. Under such conditions the 
number of eggs deposited in a given field is greatly reduced. Many 
of the eggs laid on the young growth under such conditions are 
destroyed by the grazing of the stock, and the percentage that de- 
velops is kept at a minimum. Later on it was noted that on the 
stock ranches visited the disease previously mentioned, which is com- 
mon to lepidopterous larva?, was more prevalent in pastured ranches 
than in hay ranches. The prevalence of the disease in such fields 
is due to the fact that usually a few days after stock are turned in 
the alfalfa becomes trampled. The ground and the alfalfa are very 
moist, there being more or less dew every morning, and droppings 
from the cattle bring about a foul condition in the field, thus assist- 
ing in the retention of moisture, which, in turn, is conducive to the 
development of the disease. 
If fields can be systematically and carefully pastured, damage from 
the caterpillar will accordingly be at a minimum. Cattle should 
never be allowed on a field when wet nor for too long a period, 
say from 24 to 35 days, and disking or renovating should always 
follow so as to loosen the soil and place it in a receptive condition 
for future irrigation. 
It is on ranches and fields from which successive crops of hay are 
taken that the height of the damage is reached. In such fields the 
conditions for the development of the species are as nearly ideal as 
possible, and here the worms are ordinarily unmolested in their feed- 
ing and growth. The period elapsing from the time that one crop is 
cut until another is ready for harvesting so nearly coincides with the 
length of the period necessary for the development of any one gen- 
eration of the butterfly that the cutting of the hay, as ordinarily 
carried on, does not reduce their numbers or disturb their work, 
since the worm will likely be in the adranced stage, or, perhaps, have 
passed into the pupal stage, before the crop is cut. 
CONDITIONS AFFECTING INJURY. 
As has been pointed out, this insect is ordinarily kept in control 
by its natural enemies, such as insect parasites and diseases, and it is 
only upon the occurrence of conditions unfavorable to the development 
of these enemies that serious outbreaks occur. It has also been noted 
time and again, both by the writer and others, that the seriousness 
of the damage quite often depends upon the farming methods used 
by the individual whose fields are attacked, or upon certain other 
conditions, such as character of soil, quantity of water for irrigation, 
location of land, etc. The former are conditions that the individual 
may remedy by changing his methods, while the latter may be prac- 
tically alleviated by proper handling of the farm in question. 
