72 



U.S. NATIONAL MUSEUM BULLETIN 2 55 



forms acquired a tendancy to bore into the receptacle and pedicel, 

 and from these parts into the main flower stalk where they developed 

 into true stem borers. Because the larva, at the termination of its 

 growth, was no longer precariously situated in a dehiscent fruit, but 

 instead adequately protected inside the flower stalk, pupation outside 

 of the plant (i.e., undergroimd) was no longer advantageous. Instead, 

 survival of the species was increased when the larvae began to pupate 



aenescens 



intricatus 



ochrocarus 



pulverulentus 



margmatus 



quinquepunctellus 



EXTINCT PRODOXUS 

 Diagram 2. — Relationships of the species of Prodoxus. 



within the yucca stalk. Interestingly enough, the supposed transi- 

 tion of a seed boring habit to one of stem boring is demonstrated, 

 either in part or exclusively, by those species which I have considered 

 to be the least specialized of the genus (viz., P. quinque'punctellus, P. 

 y-inversus, P. sordidus, P. marginatus, and P. pulverulentus). The 

 larvae of the remaining species are either known or thought to be 

 restricted entirely to the yucca stalk. 



