﻿232 Grossenbacher: Medullary spots and their cause 



Prunus shrubs were placed in soil in a breeding cage. On June 6 

 some more pupae were collected under both Prunus and Crataegus 

 shrubs and placed in soil in the cheese-cloth cage. On June 14 

 they looked greyish black, apparently owing to the dark color of 

 the insect inside. 



On the morning of June 17 ten very small black flies were 

 found flying about in the air space of a vessel over which cheese- 

 cloth had been tied, and some were found walking about on the soil. 

 Three were found dead and were placed in alcohol. They were 

 about 2.5 mm. long. See Figs. 2 and 3. Five flies (three females 

 and two males) were placed into a glass tube containing the distaJ 

 end of a P. avium shoot and the others into a quart fruit-jar which 

 was inverted over a short green branch of P. avium. 



Later in the day a search was made for the flies in the Prunus 

 and Crataegus thickets but none could be found. However, quite 

 a number of empty puparia were obtained from the soil beneath 

 the shrubs. On June 21 all but one of the flies in the glass tube 

 had died and it was placed in the fruit jar. The shoot in the 

 tube was found to have groups of from one to four whitish eggs 

 inserted under the periderm at the edge of a number of lenticels. 

 Twenty eggs had been deposited under the periderm around the 

 lenticels of this small twig by the three females caged with it. 



A few flies emerged from the soil in the breeding cages each 

 day until June 21 and were placed in vessels containing Prunus 

 shoots; after that date all of the puparia were found empty. By 

 June 25 most of the flies in the fruit-jar had died. The shoots were 

 carefully examined and were also found to have eggs inserted under 

 the periderm at many of the lenticels. Numerous larvae had 

 already emerged from the eggs and were mining in the cortex while 

 some had even mined as far as three centimeters in the cambium. 

 This shows that oviposition and hatching of the eggs took less thaa 

 a week. The eggs measured about 0.2X0.07 mm. 



Seedlings and sprouts of P. avium and P. domestica in a thicket 

 were found to have eggs inserted about numerous lenticels on 

 June 21. In many cases the larvae had emerged from the eggs 

 and were mining in through the cortex and cambium. But in no^ 

 instance could more than one egg be found at a lenticel. It appears 

 therefore that the deposition of eggs in the caged Prunus shoots 



