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 Kiver 

 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 larvae never being present in great numbers. 

 As noted in a separate paragraph, the destruction of the larves 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. 



