2 BULLETIN 124, U. S. DEPARTMENT OF AGRICULTURE. 



the Southwest, placing on this species the blame for injury to alfalfa, 

 were doubted. In the spring of that year, however, the writer was 

 detailed to investigate these reports in the Imperial Valley and 

 discover whether the butterflies bore any relation to the destruction 

 of alfalfa by a " green worm." His observations showed that the 

 accusations were well founded, for in July, 1910, the butterflies were 

 seen to lay the eggs that hatched into the green larvre which ate up 

 the alfalfa crop, causing a loss of thousands of dollars. 



At the end of the first year's investigation, experiments and ob- 

 servations had been completed which were thought to be of immediate 

 benefit to the ranchers in controlling the pest, and a preliminary 

 report was made and published as Circular 133 of the Bureau of 

 Entomology. During the three years subsequent to this preliminary 



V.'v" > ^<^?r~^rt^ 



Fig. 2.— The alfalfa caterpillar : Full-grown larva. Enlarged about three diameters. 



(Original, i 



investigation the writer and others have made a more exhaustive 

 study of the species, its habits, and natural or artificial methods of 

 control, and the object of this bulletin is to record these observations 

 as they have been interpreted. 



GENERAL DISTRIBUTION. 



According to Scudder 1 this insect is well distributed over the 

 United States, but is found in its greatest numbers in the Mississippi 

 Valley (see map, fig. 3) and to the westward. In only a few cases 

 does it appear east of the Allegheny Mountains, but its range ex- 

 tends northward into Canada, even as far as Hudson Bay. In 1911 

 Mr. R. A. Vickery made observations on the species at Brownsville. 

 Tex., thereby considerably extending the southern range from that 

 included in Scudder's map. In past years the species has been espe- 

 cially abundant throughout the alfalfa-growing sections where irri- 

 gation is extensively developed. 



1 Scudder. S. H. The Butterflies of the Eastern United States and Canada, v. 2, Cam- 

 bridge, 1889, pp. 1131-1132. 



