114 LEAF-MINING INSECTS 



are about 2.5 cm. long. Upon emergence they may or may 

 not feed for a short time before spinning their first moulting 

 cocoons. These initial moulting webs are said to be spun 

 on the under sides of the leaf usually over a slight depression; 

 and consist of two fabrics. A somewhat concealed aperture 

 is left through which the individual makes exit after moult- 

 ing. The webs are about tV of an inch in diameter. The 

 larvae are in retirement about twenty-four hours. 



In the second instar the larvae feed on either the upper 

 or the under surface of the leaves, devouring the tissue only 

 as far as the opposite epidermis. Irregular lesions through 

 the leaves are often formed, when, in drying, the tissue ad- 

 jacent to these feeding scars collapses. The second moult- 

 ing cocoons are begun, in southern California, during the 

 second day after the reappearance of the larvae on the 

 leaves. These webs are similar to the primary ones but 

 larger. The larvae spend a little more than a day in retire- 

 ment before appearing in the leaves in their third instar. 

 After about two days of continued feeding the larvae spin 

 the ribbed pupating cocoons. It is in this third instar that 

 the larvae feed most aggressively and do most serious injury 

 to the cotton. 



The pupal cocoons are usually spun upon some part of the 

 plant, sometimes on the leaf blade, often on its petiole, but 

 most frequently at some point along the main or lateral 

 stems. Previous to beginning the cocoon proper the larva 

 spins a series of stout upright bristles in a graceful ellipse 

 around the spot where the cocoon is to be (McGregor). 

 These may have the function of deterring the approach of 

 predaceous enemies. 



These species in general illustrate the Bucculatrix habit 

 and by varying details of host plants, color of cocoons and 

 the like, one story might apply to many. Some variations 

 from type have been noted above, namely, Chambers' state- 

 ment that B. ambrosiaefoliella, feeding on ragweed, under- 



