THE ALFALFA CATERPILLAR. 5 
As to the " cutworms," they result from the yellow butterfly, which is often 
noticed in the alfalfa fields in this valley. The butterfly lays an egg which 
hatches into the so-called " cutworm " [fig. 2] ; the latter goes into the chrysalis 
state [fig. 6], which eventually results in another butterfly. Seemingly there 
are several crops of worms which hatch in one season. Whereas we have no- 
ticed these worms and butterflies in moderate numbers for years, yet never be- 
fore have they attained the present great numbers. 
In the fall of the year 1909, after a severe outbreak in the Imperial 
Valley of California during the summer, Mr. J. A. Walton, the 
owner of a large ranch in that valley, appealed to the Secretary of 
Agriculture for methods of handling the pest. Mr. W. E. Packard, 
of the California Experiment Station, reports that the worms are- 
often quite numerous during certain years and cause more or less 
damage in the Sacramento Valley, and in the irrigated alfalfa 
regions of south-central California. Several fields that came under 
the writer's observation in 1910 made an entire failure of the third 
crop, while many others suffered a 40 to 60* per cent loss in a single 
hay crop, so that the damage for the year could be conservatively 
estimated at more than $500,000. (See PL I, fig. 1.) During that 
year (1910) there was also considerable damage in the Salt River 
Valley of Arizona, but compared with the damage in the Imperial 
Valley it was slight. In fact, as is explained in later paragraphs, 
injury was rarely as severe in any other locality as in the Imperial 
Valley. 
During 1911 the bureau was unable to make any studies in the 
Imperial Valley, but Mr. Packard, who was continually on the 
ground, told the writer in the fall of that year that little damage 
was accomplished, the larva? never being present in great numbers. 
As noted in a separate paragraph, the destruction of the larvse in 
wholesale numbers the summer before by an apparently contagious 
disease had so checked the species that it was unable to make any 
headway during that season, and, in fact, as will be seen later, it 
required two years to readjust itself to conditions. 
Throughout the season of 1911, during the writer's absence, Mr. 
E. G. Smyth, in the Salt River Valley, noted that while there was 
some damage the species was not numerous enough at any time to 
necessitate protective measures against it. 
In 1912 the writer was again located in the Salt River Valley, and 
that year, although considerable damage was done by the alfalfa 
caterpillar, the work of the disease just referred to and of parasites 
was able to keep the species pretty well within bounds, so that only 
an occasional field was seriously damaged. The following quotations 
are from the writer's own field notes : 
July 10, 1912 : Butterflies are very numerous at this time and in many fields 
are actively depositing eggs. 
