4 THE ALFALFA CATERPILLAR. 
each side, partially broken by black and red dots at each spiracle. 
There is often an intermediate, narrower, and less distinct white line 
just above each of the lateral lines. In some specimens a black or 
dark-green median dorsal line is also present. 
The pupa—tThe pupa (fig. 5) is yellowish green, has no cocoon, 
and is found head end up, attached by two threads, one of them form- 
ing a swing, to an alfalfa stalk. 
INVESTIGATIONS IN THE IMPERIAL VALLEY OF SOUTHERN CALIFORNIA. 
The investigations were begun by the author about the middle of 
March, 1910, and carried on through the summer until late in the fall 
of the same year. The writer was at first located on the J. A. Walton 
ranch, in the extreme southeastern part of the valley, and later at 
El Centro, where the work was carried on in cooperation with Mr. 
Walter E. Packard, an agent of the California 
Agricultural Experiment Station, to whom a great 
amount of credit is due for the assistance and timely 
suggestions offered. 
The Imperial Valley is a place unique 1n location 
and altitude. It is an irrigated region entirely sur- 
rounded by mountains and desert. The major part 
of the valley lies below sea level—some of it, in fact, 
as much as 250 feet below. The weather is warm 
most of the year and hot the rest of the year. It 
hardly ever rains, and the humidity is usually very 
low. The growing season extends over practically 
Naha pee the entire year, there being an entire lack of freez- 
caterpillar (Dury. ing weather during some winters. On the average 
Lessee Sas is there is not during the year more than one month 
stage. Twicenat Of weather that could be called winter weather. 
ural COTS The conditions just referred to serve to explain 
nal.) : : ° 
the immense numbers of these butterflies in the val- 
ley. The period over which the butterflies are able to continue 
breeding without being molested is very long, being from March to 
December. Then, too, owing to the very low humidity there is usu- 
ally insufficient moisture to permit the development of what appeared 
to be a contagious disease, resembling in effect flacherie of the silk- 
worm. This disease was found to be largely responsible for keeping 
this butterfly in check in other parts of the State of California and 
in southern Arizona. 
SEASONAL HISTORY IN THE IMPERIAL VALLEY. 
On the 15th of March, 1910, several adult individuals, possibly 
adults that had issued from hibernating pups, were caught in the 
act of flying over alfalfa fields and placed in a large mosquito-bar 
[Cir. 133 
