132 LEAF-MINING INSECTS 



The digitaie-mine-maker of the locust, P. robiniella, is a 

 common and widely distributed species. It attacks the 

 leaves of locusts and of other legumes. The mines may be 

 found from early summer until late fall. They are first 

 extended along the midribs of the leaves as narrow tracts 

 and then into the area on either side by a series of finger- 

 like excavations. Previous to mining the upper side, how- 

 ever, a very small subcuticular mine is made next the mid- 

 rib on the lower side. From this a passage is made to the 

 opening under the upper cuticle where the upper side mine 

 begins. During their whole period of mining the larvae 

 return to these slits and through them extrude their excre- 

 ment. Even moulted skins may be found packed in with 

 the frass in the little lowerside mines. This combination of 

 a large, clean-swept upper side mine with a small lower 

 side storage vault is distinctive, but the peculiar shape of 

 the upper side mine will alone identify these miners. 



In the later larval stages a considerable portion of the 

 parenchyma of the leaf is removed. Indeed, we have seen 

 leaves in which these mines overlapped those of Lithocolletis 

 robiniella on the lower surface of the leaf, and yet between 

 the two mines there was an unperf orated sheet of fibrovascu- 

 lar tissue and parenchyma. The mines are of a yellow 

 color; the mine of Lithocolletis robiniella is pearly white. 



The larvae leave the mines when full-fed; at that time 

 they are cylindrical and pale green, with legs and prolegs 

 well developed. In a fold of a leaf or in some crevice (or 

 even, spread out upon the glass when captured in a bottle), 

 the larvae spin a transparent somewhat flattened oval 

 cocoon. 



Cremastobombycia 



This is a small group of species whose larvae are sap- 

 feeders during the first three instars, and tissue-feeders 

 within the mine thereafter. While their mandibles are of 



