INSECTS IN RELATION TO PLANTS 



223 



FIG. 259. A wasp, Sphex ichneu- 

 mon e a, with pollinia of milkweed 

 attached to its legs. Slightly enlarged. 



tineid moth, Pronuba yuccasella, the female of which pollenizes the flower 

 and lays eggs among the ovules, that her larvae may feed upon the young 

 seeds. While the male has no unusual structural peculiarities, the 

 female is adapted for her special work 

 by modifications which are unique 

 among Lepidoptera, namely, a pair 

 of prehensile and spinous maxillary 

 " tentacles" (Fig. 260, A) and a long 

 protrusible ovipositor (B) which com- 

 bines in itself the functions of a lance 

 and a saw. 



The female begins to work soon 

 after dark, and will continue her opera- 

 tions even in the light of a lantern. 

 Clinging to a stamen (Fig. 261) 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. 262) and lays a slender egg 



alongside seven or eight of 

 the ovules. After laying one 

 or more eggs she ascends the 

 pistil and actually thrusts 

 pollen into the stigmatic tube 

 and pushes it in firmly. The 

 ovules develop into seeds, 

 some of which are consumed 

 by the larvae, though plenty 

 are left to perpetuate the 

 plant itself. Three species 

 of Pronuba are known, each 

 restricted to particular 

 species of Yucca. Riley says 

 that Yucca never produces 

 seed where Pronuba does not 

 occur or where she is excluded 

 artificially, and that artificial 

 pollination is rarely so sue- 



FIG. 260. Pronuba yuccasella. A, maxillary 

 tentacle and palpus; B, ovipositor. After RILEY. 

 Figures 260-262 are republished from the Third 

 Report of the Missouri Botanical Garden, by 

 permission. 



cessful as the normal method. 

 Why does the insect do this ? 



The little nectar secreted at the base 



