U. S. D. A., B. E. Bui. 109, Part VII. T. C. & S. P. I. I., January 30, 1913. 
PAPERS ON INSECTS AFFECTING VEGETABLES. 
THE HORSE-RADISH WEBWORM. 
(Plutella armoratia Busck.) 
By H. O. Marsh, 
Entomological Assistant. 
INTRODUCTION. 
At Rocky Ford, in the Arkansas Valley of Colorado, horse-radish 
is grown on a very limited scale for home use. Among the insect 
enemies of this vegetable are a flea-beetle, Phyllotreta pusilla Horn, 
the spinach aphis (Myzus persicx Sulz.), the common cabbage worm 
(Pontia rapse L.), the southern cabbage worm (Pontia protodice 
Boisd.), the diamond-back moth (Plutella maculipennis Curtis), and 
the horse-radish webworm (Plutella armoracia Busck). This latter 
species is a new and hitherto unrecorded truck-crop pest. As nothing 
has been published regarding its life economy the author has drawn 
up this preliminary article touching its "occurrence, life history, 
habits, and remedies. 
OCCURRENCE IN COLORADO. 
This species was first found at Rocky Ford by the author during 
the latter half of April, 1911. At this time larva?, pupae, and adults 
occurred in moderate numbers on horse-radish in one gaiden. The 
species was observed in this garden at various dates throughout 
the spring and summer. The larvae checked the early growth of 
the plants somewhat, but no serious damage resulted. In i912 the 
overwintered larvae became active on these plants, which were then 
just showing above ground during the last days of March. 
So far as the author has been able to determine, the infestation is 
limited to about 15 " clumps" of horse-radish plants in one garden 
at Rocky Ford. Careful search was made for this species on horse- 
radish in other gardens at Rocky Ford and on various species of wild 
and cultivated cruciferous plants in other portions of the Arkansas 
Valley, but without success. The infested horse-radish plants 
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