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 flamentosa cannot be introduced into the 
stigmatic tube of the flower without the help of a httle white 
tineid moth, Pronuba yuccasella, the female of which pollen- 
izes the flower and lays eggs among the ovules, that her larvee 
Fic. 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 unique 
among Lepidoptera, 
namely, a pair of pre- 
hensile and — spinous 
maxillary “tentacles ”’ 
(Fig. 256, A) and a 
long protrusible  ovi- 
positor (B) — which 
Pronuba yuccasella. A, maxillary tentacle 
and palpus; B, ovipositor.—After Ritey. Fis- combines in itself the 
ures 256-258 are republished from the Third c P 
Report of the Missouri “Botanical Garden, by Lumictions of a lance 
Borie. 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 
