10 



BULLETIN 261, U. S. DEPARTMENT OF AGRICULTURE. 



adaptation of the insect they are easily overlooked in the rearing 

 cages. 



As a rule the moths are rather inactive during the day, though egg 

 laying is by no means entirely limited to^the hours of darkness. The 

 moths are evidently active at night. Forbes (1890) records taking 

 them at night in Illinois. 



INCUBATION OF FIRST-BROOD EGGS. 



Table VI shows the incubation period of first-brood eggs. 



Table VI. — Incubation period of first-brood eggs of the plum borer, Winchester, Va., 1913. 



Number 



of eggs 



observed. 



Date- 



Period of 

 incuba- 

 tion. 



Depos- 

 ited. 



Hatch- 

 ing. 



36 

 3 

 8 

 11 

 32 

 38 

 19 



Apr. 29 

 May 2 

 3 

 4 

 6 

 7 

 8 



May 7 

 10 

 11 

 12 

 19 

 21 

 21 



Days. 



8 



8 



8 



8 



13 



14 



13 



10.3 







The shortest incubation period observed was 8 days, the longest 14, 

 and the average for seven lots of eggs was 10.3 days. The long incu- 

 bation required by the three lots of eggs deposited on May 6, 7, and 8, 

 respectively, is entirely due to the cold wave of May 8, 1913. The 

 temperatures were so extremely low that incubation very probably 

 ceased altogether. The 8-day period required by the first four lots 

 of eggs probably represents more nearly the average incubation 

 period under seasonable temperature conditions. As a rule the incu- 

 bation period for the individual eggs of a given lot varied only a few 

 hours, and in recording observations for any lot of eggs incubation 

 was considered over when the first egg hatched. 



FIRST-BROOD LARV^. 



An attempt was made to rear larvae at Winchester on plum wood. 

 A number of old plum trees were transplanted in May to the vicinity 

 of the laboratory. As the larvae hatched they were transferred to 

 these trees. All began feeding at once. Unfortunately predaceous 

 enemies and parasites destroyed all but one of these larvae before 

 they reached maturity. This larva hatched on May 7, from the first 

 lot of eggs obtained in the laboratory, spun up on June 10, pupated 

 June 12, and emerged June 22. The feeding period in this case was 

 34 days; the prepupal period, 2 days; the pupal period, 10 days. 



Two pupae taken in the field on July 14, which from their light 

 olive-green color had just transformed, emerged on July 22, indi- 



