UNITED STATES DEPARTMENT OF AGRICULTURE 
+ BULLETIN No. 966 
Contribution from the Bureau of Entomology a 
RS a L. O. HOWARD, Chief SIF Tse. 
Washington, D. C. PROFESSIONAL PAPER August 25, 1921 
THE. EUROPEAN HORSE-RADISH WEBWORM.’ 
By F. H. CHITTENDEN, 
Entomologist in Charge, Truck-Crop Insect Investigations. 
CONTENTS. 
Page. Page 
ri 1 OCT CEU Oma ee sree TU EN ECOG Ua o Mes Ta ny ak ag en ASI a vs Di a pea 8 
IDES CHUM GUO Meee een tee Carnes ett oes D INCU Allene Mee Sie ees ee 9 
Distribution ___ a2 patel aes 4 WO MBE OTS eee eae eae aS ad a 9 
Notes on occurrence and habits____~ 5 SUD NNO IM Cateye ek ST se Wa I pa 9 
istony, int North Americad=2 == ——-— 8 Pniteracuner Chtedws es ae aa 10 
INTRODUCTION. 
Horse-radish grown in the northern United States and in Canada is 
subject to attack by a medium-sized caterpillar known both as the pur- 
ple-backed webworm and the horse-radish webworm. Like so many of 
our insect pests, this species is of foreign origin and gained entrance 
into this country many years ago, but until recent years it has not been 
known to spread materially. While favoring horse-radish, it is also 
known to attack turnip and cabbage, and after feeding on the lower 
surface of the leaves sometimes webs them together near the ground. 
When abundant it attacks the stalks, even down to the roots. 
Prior to the year 1919, when this webworm was first discovered in 
injurious numbers in Virginia near the District of Columbia, re- 
ports of injurious occurrences were nearly all confined to the mart- 
time Provinces of Canada, although attack had been noted occa- 
sionally in Massachusetts, New York, New Jersey, and Wisconsin. 
The insect has been known to occur in the District of Columbia for 
several years, but heretofore it has been somewhat of a rarity. 
This species makes the third specific enemy of horse-radish inhabit- 
ing North America, the other two being the introduced horse-radish 
flea-beetle (8)?? and the native horse-radish webworm (9).‘ 
1 Bvergestis straminalis Hiibner ; order Lepidoptera, family Pyralidae. 
2 Phyllotreta armoraciae Koch. 
3 Numbers in parentheses (italic) refer to ‘ Literature cited,’ page 10. 
*Plutella armoracia Busck. 
48561°—21 
