120 LEAF-MINING INSECTS 



black spots above, and on the dorsum of the prothorax are 

 four similar, but slightly larger black spots. The head-cap- 

 sule is brownish and the body greenish gray with rows of 

 white tubercles bearing prominent hairs. 



When the parenchyma of the mine wall is consumed the 

 larvae emerge from the leaves through small holes in the 

 lower side of the mines and crawl about in search of a suit- 

 able place to pupate. Sometimes they fold over a portion 

 of the leaf border and feed there to a slight extent but more 

 often they feed no more before spinning the cocoon. Pre- 

 vious to pupation the larvae draw over a portion of the leaf 

 border by spinning silk cords from it to the leaf. They then 

 line this fold with silk and spin a sheet across the gap mak- 

 ing a firm, opaque, reddish-brown cocoon. Within the 

 cocoons they change to pupae. A week or ten days later 

 the pupal shells are thrust through the cocoon walls as the 

 adults emerge. 



Gracilaria 



This is a large genus of very similar and very variable 

 species, that are difficult of determination without knowl- 

 edge of the food plants on which they have been reared. 2 

 The young larvae of Gracilaria are all miners but most of 

 them emerge from the mine as normal larvae and feed on 

 the outside of the leaf. They never live as exposed feeders, 

 however, but make shelters for themselves by spinning silk 

 in such a way as to cause the leaf to bend or curl over them. 

 In some species the curling is clumsily done so that the 

 leaf is half crumpled. This is the case with lilac leaves 

 attacked by a common European species, G. syringella, now 

 introduced in this country. Other species make very neat 

 cones, strapping the tip of the leaf down to one border and 

 later spinning again to fold this over into a helix. Some- 



2 Forbes (1923, pp. 170-171) gives a synopsis by foods for the species of 

 the northeastern United States. 



