578 



Insects and Flowers 



FIG. 769. Pronuba-moth rubbing 

 pollen down the stigmatic tube of 

 Yucca. (After flash-light photo- 

 graph by Stevens; natural size.) 



"The full meaning of this wonderful series of operations will not be 

 understood until subsequent developments have been followed. Since the 

 process of pollination has been so thoroughly done, most of the numerous 



ovules become fertilized and the seeds 

 begin their development. In the mean time 

 the moth eggs hatch into larvae, which find 

 their food in the developing seeds. But the 

 seeds are so numerous that the larvae reach 

 their growth, gnaw a hole in the seed-pod 

 and escape, while many uninjured seeds 

 still remain in the pod. The larva spins 

 a thread by which it descends to the 

 ground, and, burrowing beneath the sur- 

 face, it passes the winter in its pupal 

 state, emerging as a fully developed moth 

 at the time of the flowering of the Yucca 

 the following summer. 



"It appears that the mature moth takes 

 no food, unless it secures some of the 

 nectar of the Yucca blossoms in which it 

 is wont to pass the day, with its head close 

 to the bottom of the flower where the nectar 



is excreted. It does not eat the pollen which it gathers, and it seems certain 

 that it is prompted to place the pollen in the stigmatic tube after each act 

 of oviposition solely by the instinct to provide for its young; for it is readily 

 understood that if the ovules are not fertilized the seeds would not develop 

 and the larvae would be without food. 



"The Yucca flower, instead of having elaborate devices to secure cross- 

 pollination, simply prohibits self-pollination by its tubular stigmas and its 

 relatively short and reflexed stamens; and then, the sticky pollen and 

 an abundance of ovules being provided, the performance of pollination 

 is intrusted to the wise instinct of the Pronuba-moth; and not pollina- 

 tion simply, but cross-pollination, for it has been noticed that it is the habit 

 of the moth after securing the pollen to fly to another flower before it begins 

 to lay its eggs." (This extraordinary interrelation between Yucca and 

 Pronuba was discovered and carefully studied by C. V. Riley in 1872, and 

 his intensely interesting detailed accounts of his observations are to be found 

 in Vol. 3 Trans. St. Louis Acad. Sci., his 5th and 6th reports as state ento- 

 mologist of Missouri, and in the 3d Ann. Rept. of the Missouri Botanical 

 Garden). 



The above various and interesting examples of the interrelations between 

 flowers and insects are not exceptional cases; indeed this state of affairs 



