258 LEAF-MINING INSECTS 



peculiar habit of hovering like syrphus flies before alighting. 

 The females further have a habit of puncturing the leaves 

 with their ovipositors and turning about and sucking the 

 juice with their mouths. It is a common sight to see leaves 

 covered with these small feeding punctures. 



The eggs are laid in the tissue of the leaf, probably from 

 the upper side. The larvae are solitary miners although 

 several may be found within a single leaf. The mine is at 

 first linear, turning and twisting considerably and often 

 threadlike. Later it expands into a blotch. When several 

 larvae mine on a single leaf the mines anastomose so that it 

 is difficult to trace the course of the mines. The frass occurs 

 in a broken line down the center of the mine becoming some- 

 what scattered in the blotched portion of the mine. When 

 the larve is mature it cuts a slit at the edge of the mine 

 through which it escapes. The puparium is formed out- 

 side the mine. There is probably only one generation during 

 the summer. 



NAPOMYZA 



Of the few European species included in this genus one 

 N. lateralis 2 may occur as a leaf miner in the sowthistle, 

 Sonchus oleraceus, in North America. It has been little 

 studied. The best account of it is the brief one that was 

 published by Goreau in 1851. He said that the larva makes 

 a filiform curving mine, which gradually widens from its 

 origin; that it is solitary, that it grows rapidly and is com- 

 mon; that it finally comes to rest against the lower epi- 

 dermis of the leaf where it changes to a yellowish puparium. 



CERODONTA 



A single leaf -mining species, C. femoralis, infests the leaves 

 of corn and other grains and grasses. It was called the corn 



2 The early records of P. lateralis Fall in this country are referable to 

 Phytomyza chrysanthemi Kowarz. 



