12 BULLETIN 432, U. S. DEPARTMENT OF AGRICULTURE. 



A number of these galleries are often found leading away from 

 one mine in a leaf. All sorts of peculiarly shaped mines are made 

 in leaves, especially in small plants or in plants with a limited amount 

 of leaf surface. Some of these mines show almost perfect loops, 

 while others traverse the leaves in snakelike fashion. 



In young oats and barley the larvae apparently break away from 

 the accustomed habit of making threadlike mines and instead appear 

 to undermine almost the entire upper surface of the leaves in which 

 they are feeding. As a result the leaves dry up (PL II, fig. 4). 



The larvae of this species pupate in the mines, usually in the leaf 

 sheath (PL I, fig. 5). The adult, upon emerging from the puparium, 

 tears open the dry tissue at or near the pupal case and makes its 

 escape. 



LENGTH OF LARVAL STAGE. 



The average length of the larval stage in the latitude of Columbia, 

 S. C, is 10 days during midsummer or in seasons of high tempera- 

 tures. This period is considerably longer in spring, and much longer 

 in late fall, ranging from 9 to 24 days during different seasons and in 

 different localities. 



Larvae hatching from eggs about the middle of October were 

 overtaken by frost and killed the second week in November. Larvae 

 hatching from eggs deposited the same day by the same fly some- 

 times show a difference of three days in their total period of larval 

 development. The difference is apparently caused by a deficiency 

 in the immediate supply of food, which forces the larva to mine a 

 greater area to satisfy its demand, and as a result the duration of 

 the period of larval development is lengthened. 



LENGTH OF PUPAL STAGE. 



The length of the pupal stage (PL I, fig. 4; PL II, fig. 7) of this 

 insect varies from 9 to 12 days during midsummer and from 11 to 

 16 days during spring and late fall in the latitude of Columbia, S. C. 



A short pupal period of eight days during July is recorded by 

 G. G. Ainslie at Nashville, Tenn., and a pupal period of from 14 

 to 18 days by V. L. Wildermuth at Tempe, Ariz., during March 

 and April. At Pasadena, CaL, the pupal period ranges from 12 to 

 24 days at different seasons of the year. 



LIFE AND HABITS OF ADULTS. 



Flies begin to issue from puparia during the latter part of May 

 in the latitude of La Fayette, Ind., but probably considerably earlier 

 at Columbia, S. C, as adults in breeding cages began to issue in 

 February of 1915. These, however, died within a short time and 

 without reproducing. In the vicinity of Pasadena, CaL, adults of 



