﻿230 Grossenbacher: Medullary spots and their cause 



paper, to the effect that "Agromyza pruinosa remains in the pupal 

 stage in the ground during winter" applies to the fly which he and 

 Brown studied it certainly differs from the one discussed in this 

 paper. The Prunus miner, as noted above, was found to hibernate 

 in the cambium of the host during the winters of 1910-1 1 and 191 1- 

 12 in the larval stage and to pupate early the following summers. 



Life history of the Prunus miner 

 On pages 63-65 of my paper on medullary spots cited above 

 are described the early stages of a cambium miner that feeds in 

 Prunus and Crataegus but does not attack Salix. The observa- 

 tions upon which that discussion was based extended from August 

 15 to November 15, 1910; or to the time when the cambium had 

 dormancy forced upon it by the early cold weather of western 

 New York. The larvae continued mining until nearly mid- 

 November but were mostly still under six millimeters in length 

 when they ceased feeding. 



In 1911 the first careful examination and the first large collec- 

 tion of miners was made on May 21. They had apparently 

 been active for some time. The mines were most numerous in the 

 thicker parts of the infested shrubs. The channels were larger 

 than the ones made by the same larvae in the 1910 growth, as was 

 readily seen by tracing them back to the previous year's growth. 

 The larvae still fed with their lateral sides toward the wood and 

 bark, but the end turns in their mines were both clockwise and 

 counter-clockwise. In the stem near the ground the return trips 

 were often only a decimeter or two in length resulting in a zigzag 

 course, but some of them still were making trips 1.6 meters in 

 length. About a fourth of the larvae had left their hosts by boring 

 their way out through the bark. The holes were still open and could 

 be readily seen once they had been found. The larvae usually 

 came out through the bark a centimeter or more after making a 

 lower turn. Some exit holes were found as high as a meter above 

 but most of them were within two to four decimeters of the ground ; 

 others entered the cambium of the crown and roots before mining 

 their way out. In many instances mines had been made downward 

 to about the surface of the ground and then turned distad or upward 

 a decimeter or more before making an exit. Several larvae were 



