U. S. D. A., B. E. Bui. 109, Part VII. T. C. & S. P. 1. 1., January 30, 1913. 



PAPERS ON INSECTS AFFECTING VEGETABLES. 



THE HORSE-RADISH WEBWORM. 



(Plutella armor acia Busck.) 



By H. 0. Marsh, 

 Entomological Assistant. 



INTRODUCTION. 



At Rocky Ford, in the Arkansas Valley of Colorado, ho:se-radish 

 is grown on a very limited scale for home use. Among tie insect 

 enemies of this vegetable are a flea-beetle, PJiyllotreta pusilh Horn, 

 the spinach aphis (Myzus persicse Sulz.), the common cabbage worm 

 (Pontia rapse L.), the southern cabbage worm (Pontia pntodice 

 Boisd.), the diamond-back moth (Plutella maculipennis Curtis) and 

 the horse-radish web worm (Plutella armoracia Busck). This litter 

 species is a new and hitherto unrecorded truck-crop pest. As notiing 

 has been published regarding its life economy the author has dnwn 

 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 larvas, pupas, and adults 

 occurred in moderate numbers on horse-radish in one garden. 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 1912 the 

 overwintered larva? 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 u 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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