Wes. D. A. B- E. Bul. 82) Part V. Issued August 31, 1910. 
SOME INSECTS INJURIOUS TO TRUCK CROPS. 
BIOLOGIC AND ECONOMIC NOTES ON THE YELLOW-BEAR 
CATERPILLAR. 
(Diacrisia virginica Fab.) 4 
By H. O. Marsu, Agent and Expert. 
RECENT INJURY. 
During the late summer and fall of 1909 there was a serious out- 
break of the common yellow-bear caterpillar (Diacrisia virginica 
Fab.) in the upper Arkansas Valley of Colorado. Never before in 
the history of the valley had this species been so destructive, and 
the outbreak came as a surprise to all concerned. 
The larve, or caterpillars, of the first generation developed nor- 
mally on weeds along the fences and irrigation ditches and caused 
little damage to cultivated crops, but the larve of the second gener- 
ation, which began to develop about the middle of August, were so 
numerous that the weeds were not sufficient to support them and 
they spread to sugar beets and other crops. 
The sugar beets, because of the extensive acreage and the large 
supply of food which their tender foliage offered, were more severely 
damaged than any other crop. The larve were variously estimated 
to have infested from 15,000 to 20,000 acres of sugar beets in the 
upper portion of the Arkansas Valley. Definite records from this 
vast acreage show that fully 1,006 acres were badly defoliated. 
The larvee of this second generation developed so late in the season 
that the injury to which the beets were subjected did not noticeably 
reduce the tonnage, but all over the worst infested area there was a 
reduction in sugar content and quality. Owing to the other factors, 
such as late rains and a disease known as “leaf spot” (Cercospora 
beticola Sacc.), which also tended to lower the sugar content, any- 
thing more definite than an approximate statement concerning the 
loss of sugar in the beets would be very misleading. However, 
estimates based on comparative analyses made by the chemists at 
a4 Formerly known as Spilosoma virginica Fab. 
59 
