264 



ENTOMOLOGY 



Yucca. An extraordinary example of the interdependence 

 of plants and insects was made known by Riley, whose 

 detailed account is here summarized. The yuccas of the 

 southern United States and Mexico are among the few plants 

 that depend for pollination each upon a single species of insect. 

 The pollen of Yucca filament osa cannot be introduced into the 

 stigmatic tube of the flower without the help of a little white 

 tineid moth, Pronuba yuccasella, the female of which pollen- 

 izes the flower and lays eggs among the ovules, that her larvae 



FIG. 256. 



may feed upon the 

 young seeds. While 

 the male has no un- 

 usual structural pecu- 

 liarities, the female is 

 adapted for her special 

 work by modifications 

 which are u n i q u e 

 among Lepidoptera, 

 namely, a pair of pre- 

 hensile and spinous 

 maxillary " tentacles " 

 (Fig. 256, A) and a 

 long protrusible ovi- 

 positor (B) which 

 combines in itself the 

 functions of a lance 

 and a saw. 



The female begins to work soon after dark, and will con- 

 tinue .her operations even in the light of a lantern. Clinging 

 to a stamen (Fig. 257) she scrapes off pollen with her palpi 

 and shapes it into a pellet by using the front legs. After 

 gathering pollen from several flowers she flies to another 

 flower, as a rule, thrusts her long flexible ovipositor into the 

 ovary (Fig. 258) and lays a slender egg alongside seven or 

 eight of the ovules. After laying one or more eggs she ascends 



Pronuba yuccasella. A, maxillary tentacle 

 and palpus; B, ovipositor. After RILEY. Fig- 

 ures 256-258 are republished from the Third 

 Report of the Missouri Botanical Garden, by 

 permission. 



