206 LEAF-MINING INSECTS 



separated by thin flat expansions at the lateral margin. 

 The adult beetles feed upon the leaves. When their eggs 

 are mature the females bore oval holes through the epider- 

 mis with their beaks and then oviposit in the holes. 



Perhaps the most interesting thing about the leaf-mining 

 weevils is the cocoon which some of them make. Many 

 beetles form a pupal cell of earth or wood by pushing about 

 loose materials surrounding them, but few indeed spin co- 

 coons of silk as these do. If we pick up one of these larvae 

 which has begun to spin its cocoon we may notice that the 

 thread of silk issues, not from the mouth as in caterpillars, 

 but from the anal opening. 



Traegardh has shown in the case of Orchestes quercus that 

 the malpighian tubules are very large. These appear to be 

 the source of the fluid silk. The conical and rather sharply 

 pointed final body segment is used as an implement for 

 distributing and fastening threads of silk. The completed 

 cocoons are nearly spherical in form and are of a firm strong 

 texture, well fitted for protecting the delicate pupae within 

 them. 



In North America, leaf-mining weevils apparently occur 

 in but two genera, Orchestes and Prionomerus. There is 

 in Europe, a species Cionus olens, which mines the young 

 leaves of various mulberries, making a puffed mine in which 

 it afterward spins a rounded cocoon. Then Bargagli men- 

 tions Rhamphus aeneus and Brachonyx pineti as miners. 

 The latter lives in the needle-like leaves of the Scotch fir, 

 Pinus sylvestris. There are, too, a few species of Apion 

 which mine in the midribs of fleshy leaves, as of thistles, 

 sunflowers, sorrels and others. 



Prionomerus 



Of this genus only a single species occurs in northeastern 

 North America. It is the sassafras mining weevil, P. calcea- 

 tus, and it ranges with its host plants, the sassafras and tulip 



