248 LEAF-MINING INSECTS 



have small tubercles on the lateral aspect of the last segment. 

 There are two lateral tubercles in A. parvicornis, and one in A. 

 melampyga. No tubercles have been found in Phytomyza. 



The pupa. The pupa is formed inside the hardened 

 larval skin or puparium, and this turns brown or black, as 

 usual, but shows distinct and rather deep intersegmental 

 constrictions along the sides, with anterior and posterior 

 spiracles projecting at the ends. 



The adult. The adults are small blackish or yellow marked 

 clearwinged flies generally a quarter of an inch or less in 

 expanse of wings, as shown by our table on page 241, this 

 family contains the bulk of the leaf -mining species of Diptera. 



The females of certain Agromyzidae have a peculiar way 

 of puncturing the leaves of the host and feeding on the 

 juices. One of us (Frost) has observed this in several species 

 of the genera Agromyza and Phytomyza. It may be that 

 all of the Agromyzidae feed in this manner, but it has been 

 observed in only a few species. The ovipositor is elongated 

 and is especally adapted for inserting the eggs within the 

 tissues of the leaf, but it serves equally well in making feed- 

 ing punctures. After making a puncture in the leaf, the 

 female turns about and sucks the juice through the hole. 

 The feeding punctures are usually large and very conspicu- 

 ous. Some species, however, make very small punctures 

 which resemble the feeding punctures of mites or thrips. 



Some species of Agromyzidae issue from their winter 

 quarters in spring, as early as April or by the first of May. 

 Others do not appear until June or July. Several species 

 have but one generation a year, and this appears in the spring. 

 It is impossible to obtain either larvae or adults of these 

 species toward the middle of summer. Other species have 

 several generations, and are active throughout the entire 

 summer. These keep the leaves continually covered with 

 fresh mines. 



