TORTRICOIDEA, PYRALIDOIDEA AND NOCTUOIDEA 179 



to new lily leaves completely buried themselves in four 

 hours. Usually but one larva occupies a mine. Several 

 instances were observed, however, in which two were occu- 

 pying the same mine and in one heavily infested leaf eight 

 larvae of about the same size were found in a single, large 

 mine. The formation of the mine is due primarily to the 

 fact that the larva apparently uses only the parenchyma as 

 food and must get under the epidermis in order to get it. 



Several days after the mine has been formed the upper 

 and lower epidermis bounding it begin to disintegrate, ulti- 

 mately leaving an ugly hole in the leaf and, in badly infested 

 leaves, producing numerous perforations. The effect on the 

 plant is evident. Not only is the leaf disfigured but in 

 proportion to the number of holes present the leaf surface 

 is also reduced. Many cases were observed in which the 

 infestation was great enough to cause the death of the entire 

 leaf. 



By the end of the second instar the larvae are too large 

 to continue as miners in the leaf blade. They then travel 

 to the midrib, often to the base of it, either openly creeping 

 upon the surface, or cutting slits as they go through the 

 leaf tissue; they bore into it, always downward, and thence 

 down the petiole. The length of the burrow in the petiole 

 varies according to the time it has been inhabited, and to 

 some extent according to the size of the larva. Burrows 

 were frequently two feet long and occasionally longer. 



In the field the best mark of recognition of the work of 

 these larvae is the heap of excrement which accumulates 

 around the margin of the burrow on the upper side of the 

 leaf. As would be expected the quantity depends upon the 

 length of occupancy and the activity of the larva. In 

 August it was a common thing to find hundreds of leaves 

 with conspicuous heaps of excreta around the hole on the 

 upper surface. The excrement is always deposited outside 

 of the burrow. 



