90 LEAF-MINING INSECTS 



sixth inch in length, greenish white in color with the head light 

 brown; the contents of the alimentary canal show through the 

 semitransparent body wall as a greenish or brownish stripe. 



After entering the leaf the 3 r oung larva eats out a narrow linear 

 burrow, or mine, an inch or less in length, leaving the outer layers 

 of the leaf intact. This part of the mine usually follows a tortuous 

 course but may be nearly straight. The larva next enlarges its 

 mine into an irregular ovate blotch about one half inch in length. 

 In the linear part of the mine the excrement is left as a blackish 

 streak extending along the center of the burrow; in the blotch 

 mine it forms a broad, irregular band along the center, but does 

 not extend to the tip. The outer leaf layers overlying the mines 

 turn brownish or yellowish; the upper layer seems to be thinner 

 than the lower, and the mines are more conspicuous when viewed 

 from above. There are often ten or a dozen mines in a single 

 leaf (pi. 1, fig. 3). 



When full grown the larva leaves the mine through a cut in the 

 upper surface of the leaf, falls to the ground, and there constructs 

 a small flattened brownish cocoon in cracks in the soil, under loose 

 stones, or between the base of the tree and the surrounding soil. 

 Where the ground is undisturbed, the cocoons are rarely found 

 more than an inch below the surface. Sod furnishes ideal winter 

 quarters for the cocoons. 



The adult of the plum leaf -miner is a small bronzy black 

 moth having an expanse of 7 to 5 inch. The f orewings are 

 crossed by a shining white band on the outer third, and the 

 head bears a conspicuous orange tuft. 



The work of an apple- and pear-leaf infesting species, iV. 

 pomivorella, is thus described in Slingerland and Crosby's 

 Manual of Fruit Insects, page 74 : 



The tiny, dark, emerald-green caterpillars, about T V inch long, 

 m ake narrow, tortuous or serpentine mines, often 2 inches in 

 length and less than i\ inch wide just beneath the upper surface 

 of the leaves of the apple and pear. The first half or two-thirds 

 of the mine is broader and nearly filled with a continuous zigzag- 

 zing thread of black excrement. The insect is quite common in 



