274 LEAF-MINING INSECTS 



Two of the docks, Rumex crispus and R. obtusifolias, are 

 extensively mined by several species of Pegomyia. Among 

 these are two, P. calyptrata Zett, and P. vanduzeei Mall., 

 which occur commonly throughout the United States. 

 P. calyptrata is by far the commoner of the two species. 

 The adult is readily distinguished by a bluish gray thorax 

 and a reddish yellow abdomen. P. vanduzeei, on the other 

 hand, is less common. It occurs about Ithaca, New York, 

 abundantly in the early smmmer, but later in the season 

 neither eggs, larvae, nor adults have been found. This 

 species is distinguished by its inconspicuous gray color. 

 The eggs of the dock miner are seldom laid singly, but are 

 usually in groups of from three to five, or occasionally in 

 groups of six or seven. They are normally placed in neat 

 transverse rows on the under surface of the leaf. 



The number of eggs occurring on a single leaf is surprising. 

 As a rule one finds only five or six groups, but it is not un- 

 common to find more. In one instance twenty groups of 

 eggs were found on a single leaf, 65 eggs in all; on another 

 leaf, 16 inches long, eighteen groups containing 47 eggs. 

 Not all the larvae from these eggs mature within the leaf 

 on which they are laid, but some migrate and start new mines 

 on other leaves. 



The eggs hatch in from two to six days and the young 

 larvae immediately enter the leaf, making small holes through 

 the lower epidermis. All the eggs of a single group hatch 

 at the same time and the larvae feed in a common mine, 

 which is at first linear. The larvae mine side by side, pro- 

 gressing only in a forward direction. They keep close to- 

 gether, and all change their direction of mining at the same 

 time, leaving behind them a short linear path. In about a 

 day, although no definite time can be set, the larvae begin 

 to enlarge their mine laterally, forming a blotch. They 

 still remain in a common mine but separate in different 



