﻿234 Grossenbacher: Medullary spots and their cause 



On July i6 the new generation of cambium miners was found 

 to be rather few in number as compared with the large number 

 of eggs and young that were present in late June. Possibly the 

 excessive and very long drought in connection with the un- 

 precedented hot weather in western New York during the latter 

 part of June and the first part of July (191 1) reduced cambial 

 activity to such an extent as to make mining difficult and resulted 

 in the death of many larvae. 



Comparison of the Prunus and other dipterous cambium 

 miners 

 When the Hfe history of this Prunus miner is compared with that 

 recorded by Nielsen for Agromyza carbonaria and with that given 

 by Greene for A. pruinosa, as well as with the fragmentary history 

 published by Kientz (discussed in my earlier paper) , it becomes 

 evident that though these miners are similar in many ways they 

 must be different species. A . carbonaria and A . pruinosa pass the 

 winter in the pupal stage in the ground while the Prunus miner 

 goes through winter in the cambium of the host as a larva. The 

 fact that the Prunus miner was never found in willows growing 

 among infested Prunus, as recorded in my earlier paper, also goes 

 to show that the insect so commonly present in Salix and Betula 

 is not identical with the Prunus miner. In addition to the above 

 noted and irreconcilable differences in the life histories and hosts 

 of the miners there is a marked difference in the size of all the 

 stages of the Agromyza pruinosa discussed by Greene and others 

 and those of the one described in this paper. The most striking 

 difference is to be found in the length of the larvae just before 

 pupation : The measurements given by Greene and others for the 

 fully grown larvae studied by them are 20-30 mm. while those 

 of the fly under consideration here are only 11-13 mm. in length. 

 The larvae of A. carbonaria also measure about 20 mm. in length; 

 and besides, Nielsen calls especial attention to the reduction in 

 the number of plate-girdles preceding pupation which does not 

 hold of the miner of Prunus. The Prunus miner retains all the 

 girdles at least to within a day of pupation. The adults of A. car- 

 bonaria and A. pruinosa as given by Nielsen and by Greene are 

 also larger than these. The venation of the wings figured by 



