THE ALFALFA CATERPILLAR. 9 
caterpillar, never eating alfalfa as long as it could find the larve or 
pup of Eurymus around. 
One of these larve ate 5 larvee of the Eurymus during a single day, 
and on May 25 the writer counted many dozens of pupal cases in the 
field that had the contents eaten out. Each case had an irregular 
opening eaten into it; sometimes the end of the abdomen would be 
eaten away, and again the opening would be on the side, often the 
entire side being destroyed. Upon further search the larve of Helio- 
this were found in the act of devouring the pup and were thus 
responsible for the damage. 
OTHER NATURAL ENEMIES. 
Larval disease—The most common natural enemy observed was a 
supposedly contagious disease which there has not yet been an oppor- 
tunity to carefully study. This was prevalent all over the valley 
and is present at all seasons. It destroys both the pupa and larva. 
but more often the larva. The worms when attacked by the disease 
turn a lighter green, become sluggish, and in a day or two are nothing 
but a soft, decayed mass, usually found hanging to the alfalfa stalks. 
The development of the disease apparently depends upon moisture, 
as it is more often noticed in moist fields. The fact that it does not 
at all times keep the worms in 
suppression is without a doubt 
due to the fact that the climate 
of the Imperial Valley is very 
dry. Larve brought to the | Pie 
= : Fic. 8.—Bollworm (Heliothis obsoleta), an 
laboratory for rearing of insect enemy of the alfalfa caterpillar. Twice 
parasites and for life-history nebutarsizes  Mniemal) 
studies in a large percentage of cases died of the disease as soon as 
confined. A quantity of worms sent to Berkeley, Cal., by Mr. Wilsie, 
of the Imperial Valley horticultural commission, for experimental 
rearing of parasites, all died of the disease, either before reaching 
their destination or the day after. During the first week of July the 
humidity was exceptionally high for the Imperial Valley, and at the 
time about 95 per cent of the larve in the valley succumbed to disease, 
thus saving a hay crop for a great many of the farmers, but stopping 
experiments almost completely. It is probable that this disease has 
occurred in years past, and it may occur in future years, at some time 
during the summer season, in such abundance as to destroy a brood, 
as it did in'the past vear (1910). 
It seems to be partly due to this disease that the alfalfa cater- 
pillar does not appear in such large numbers in other regions of the 
Southwest, notably in alfalfa regions in Arizona. Here there seems 
to be greater humidity and more moisture, and the disease is able to 
keep the number of worms reduced to a minimum. 
[Cir. 133] 
