72 



PAPERS ON INSECTS AFFECTING VEGETABLES. 



have been in their present location for several years and it is impos- 

 sible to determine their origin or whether they were infested when 

 planted in the garden mentioned. 



GENERAL APPEARANCE AND HABITS. 



The horse-radish webworm (fig. 25) is a beautiful, slender moth 

 belonging to the lepidopterous family Yponomeutidae. The wings are 

 cream colored with a brownish tinge and have an expanse of about five- 

 eighths of an irch. The moths are shy and hide among the foliage of 

 infested horse-radish plants. When disturbed they fly readily for a short 

 distance and usually promptly hide. In captivity they feed eagerly on 



diluted honey. 



The eggs (Rg. 26, c) 

 are scale like and are 

 usually deposited 

 singly on the upper or 

 lower sides of the 

 leaves. 



Fig. 25. — The horse-radish webworm (Plutella armoracia): Moth, 

 side view, above; moth with wings spread below. Enlarged. 

 (Original.) 



Fig. 26. — The horse-radish web- 

 worm: o, Larva, lateral view; 

 b, larva, dorsal view; c, egg. 

 All enlarged. (Original.) 



The newly hatched larvae are pale yellow. The mature larvse 

 (fig. 26, a, b) are yellowish green, with a more or less distinct yellow 

 or orange band across the dorsal surface near the middle. Almost 

 immediately after hatching the larvse spin compact webs under 

 which they rest and feed until mature. The webs are white or gray 

 and are remarkably close-meshed. When the horse-radish plants 

 are young the larvae web together and feed on the first spikelike 

 leaves and later a favorite location is among the blossom buds. With 

 older plants the larvae feed on the leaves generally, usually selecting 

 the most tender ones. 



