Mar. 3, 1919 



Species of Pegomyia Mining Dock 



241 



Table VI. — Incubation period of the eggs of Pegomyia affinis 



Experiment No. 



Eggs laid. 



Eggs 

 hatched. 



Length 

 of stage. 



A115 

 A119 

 A125 

 A130 

 A131 



May II 



May 14 



May 18 



May 24 



May 25 



May 16 

 May 21 

 May 24 

 May 28 

 ..do 



Days. 



IvARVA. — The eggs hatch in from three to seven days. All the eggs 

 of a single group hatch at the same time, and the young larvge feed to- 

 gether in a common mine. At first this is linear, but soon the larvae 

 separate in different directions and a blotch mine is formed which ob- 

 scures the original linear track. The mines produced on the leaves 

 can not be distinguished from those of P. calyptrata. 



Table VII. — Length of the larval period of Pegomyia affinis 



Experiment No. 



A2... 

 A124. 

 A124. 



Eggs 

 hatched. 



May 

 May 

 ..do. 



A127 May 22 



A143 May 31 



Puparium 

 formed. 



May 23 



June 6 



Jtine 8 



June 7 



June 13 



Length 

 of larval 

 period. 



Days. 

 12 

 16 

 18 

 16 

 13 



From Table VII it will be seen that the length of the larval period 

 varies from 12 to 18 days. A larger number of records would, perhaps, 

 show even greater variation. This variation is due, as in case of P. 

 calyptrata, to weather conditions. 



The mature larvae escape from the leaves through the cracked surface 

 of the dried and parchment-like mine. If the ground is not too hard, 

 they penetrate to a depth of 2 or 3 inches; otherwise, they form their 

 puparia beneath leaves or rubbish. 



Number of generations. — ^The writer is uncertain as to the number 

 of generations. At first he confused the two species mining dock and 

 thought there was but one. Later he noticed his mistake, but it was 

 then too late to make definite observations. The few notes made seem 

 to indicate that there are but two generations a year. A portion of the 

 first-generation adults issued in from 12 to 18 days; the rest overwin- 

 tered as puparia and issued the following spring. It is believed that all 

 of the second generation overwinter as puparia and issue the follovdng 

 spring. This seems to be the case, because the eggs and larvae of this 

 species were not found after the end of June. 



