UNITED STATES DEPARTMENT OF AGRICULTURE 



BULLETIN No. 966 



Contribution from the Bureau of Entomology 

 L. O. HOWARD, Chief 



^^Jf-'^^U 



Washington, D.C. 



PROFESSIONAL PAPER 



August 25, 1921 



THE EUROPEAN HORSE-RADISH WEBWORM/ 



By F. H. Chittendkn, 

 . IJnloiiiologist in Charge, Truck-Crop Insect Invcstiyationn. 



CONTENTS. 



Page. 



Introduction 1 



Description i; 



Distribution 4 



Notes on oecurreucc and habits 5 



History in North America S 



Page. 



Food plants .- 8 



Natural enemies 



Control 9 



Summary 9 



Literature cited 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 pes^ts, this species is of foreign origin and gained entrance 

 into this country man}- Aears ago, but until recent 3'ears it has not been 

 laiown to spread materially. While favoring horse-radish, it is also 

 knowm 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 tlie year 1919, when this webw^orm was first discovered in 

 injurious numbers in Virginia near the District of Columbia, re- 

 ports of injurious occurrences were nearlj'^ all confined to the mari- 

 time Provinces of Cana<1a, although attack had been noted occa- 

 sionally in Massachusetts, Xew York, New Jersey, and Wisconsin. 

 The insect lias been knoAvn 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 (<9)-=' and the native horse-radish Avebworm {9).^ 



' Ercrf/rstis stnimiiialix Hiibnor : order Lopidoptera, .family Pyralidae. 

 ^ Ph i/Ilotrcta armnrtiriar Koch. 



'^ NuniUers in parentheses (italic) refer to "Literature cited." page 10. 

 * Plutclla armoracid Busck. 

 48501°— 21 



