THE EMERGENCE OF PRONUBA FROM THE YUCCA CAPSULES. 



BY J. C. WIIITTEN. 



Studies of the eastern Yucca Moth (Pronuba yucca- 

 sella), and its importance in yucca pollination, have, from 

 time to time, been recorded in the Garden Reports.* Here- 

 tofore, a knowledge of the life history of this interesting 

 insect has been incomplete in one detail, observations hav- 

 ing left a break from the time when the larva ceases feeding 

 in the capsule, until it is incased in its underground cocoon, 

 where, the following spring, it is to change to the pupa 



state . 



The past season, through suggestions of the Director of 

 the Garden, steps were taken to ascertain the time and 

 method of the passage of the insect from the capsule to 

 the ground. Two plants of the common Yucca filamen- 

 tosa were selected for observations. These yuccas bloomed 

 about the last of June. On August 5th, perforations were 

 seen, where a few of the larvae had left the capsules. To 

 prevent other larvae from escaping unnoted, a bag was 

 fastened closely around the scape of each plant, the top of 

 the bag being held open by a large hoop, which surrounded 

 the plant just below the seed pods. These bags were held 

 in place by stakes driven into the ground, and insured 

 catching any larvae that might drop from the pods. To 



* 



prevent their crawling out of the bag, its upper edge was 



coated with tar. 



Observations were regularly made morning and evening, 



from August 5th to August 12th. Up to the evening of 

 the 10th, no larvae had made their appearance. The 

 w T eather, meantime, was dry and hot. During the night 



* Pp. 99 to 158, pi. 34 to 43, Third Garden Report; pp. 181 to 225, pi. 



20 to 23, Fourth Garden Report. 



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