24 INSECTS 



vations of Dr. C. V. Riley, erstwhile Entomologist to 

 the U. S. Department of Agriculture. 



The flowers of the species of Yucca are absolutely 

 incapable of self- or wind-pollination, and the stigma is 

 so situated that no ordinary insect visitor can reach it 

 in a casual search for food. In some localities, it was 

 observed that the common Yucca or soap-weed never 

 produced seed and that wherever seed was produced, 

 almost every pod was infested by a little caterpillar 

 that destroyed a greater or less percentage of the seeds. 

 The parent of this caterpillar is a small white moth, 

 the Pronuba ynccasella of Riley, in which the mouth- 

 parts are curiously modified and utterly unlike those of 

 any other moth species that we know. At the sides of 

 the ordinary tongue there are developed a pair of flex- 

 ible processes set with little pegs and spines, and capable 

 of being coiled like the tongue itself. When the female, 

 which alone has these processes, is ready to lay an egg, 

 she enters a Yucca blossom, gathers a little mass of 

 pollen, rolls it into a ball, carries it by means of the 

 coiled processes to the pistil, and rams it down so as 

 to bring it into direct contact with the receptive surface. 

 Not until this has been completed does she turn and 

 then, into the ovary or embyro seed pod, she forces an 

 egg by means of a slender, sharp-pointed ovipositor. 

 She is now ready to repeat the process on another flower 

 and she does repeat it until her stock of eggs is exhausted. 

 Here we have a deliberate pollination preceding ovi- 

 position, as if the insect knew that it would be useless 

 to lay an egg until the possibility of development in 

 the seed pod was assured. 



This peculiarity, though confined so far as we know 

 to the genus Pronuba, is not confined to one species 

 only. There are a number of Yuccas in the country, 

 including the giant or tree Yuccas of the southwest, 



