128 LEAF-MINING INSECTS 



The leathenvood leaf-miner, L. dircella, mines the leaves 

 of Dirca palustris. It makes large, white blotches on the 

 upper surface and from one to eight larvae may be found 

 in a single mine. When the larvae are gregarious in a mine 

 most of the leaf is involved and the several individuals 

 occupy finger-like projections at the borders of the mine. 

 Larvae may be found in the leaves in June and in Septem- 

 ber in the latitude of southern Ohio. The cocoons are spun 

 outside of the mine. 



The hog-peanut leaf -miner, L. amphicarpeaefoliella, mines 

 the leaves of Falcata monoica and F. pitcheri from August 

 to October. The larvae make creamy white blotches cov- 

 ering most of the upper surfaces of the leaves. When full-fed 

 they cast their last moult skins and emerge to spin cocoons 

 in withered leaves or on the ground. 



Marmara 



This is a genus of about a dozen North American species, 

 whose flat, sap-feeding larvae are miners for the most part, 

 not in leaves but under the cuticle of young twigs or of 

 semi-herbaceous stems. Two species are leaf-miners, and 

 a third mines under the cuticle of the joints of prickly pear 

 (Opuntia): these joints are functionally comparable with 

 leaves. One species, M. pomonella, has been recorded by 

 Knight (1922) as damaging the appearance of apples by 

 mining their surface when green (see pi. 2, fig. 4). 



A possible explanation of their departure from family 

 habit is that, in the course of evolution, the seasonal develop- 

 ment became so changed that the maturation of eggs was 

 no longer synchronous with the leafy season of the host 

 plants, and that the adults met the emergency by oviposit- 

 ing on the next most succulent part. Certain it is that M . 

 salictella now mines willow shoots and M . fulgidella the 

 branches of oak in the early spring before the leaf buds have 

 opened. Also, the species, that are leaf-miners have, as 



