108 
PARK AND CEMETERY. 
THE YUCCA AND THE YUCCA MOTH 
The Missouri Botanical Garden at St. 
Louis has a valuable collection of hardy 
Yuccas, and the garden bulletin for June 
contains an interesting discussion of the 
Yucca and the Yucca moth. 
in Europe, was struck with the fact that 
Yuccas rarely ever fruited in that country. 
He already knew that specimens and re- 
ports from collectors on the Atlantic coast 
and the Western plains, where various 
YUCCA FLACCIDA GLAUCESCENS. 
One of the first students of the Yucca 
and its associated insect was Dr. George 
Engelmann fittingly styled the pioneer bot- 
anist of the West, a resident of St. Louis 
and with whom the early history and 
foundation of the Missouri Botanical Gar- 
den is so closely associated. Dr. Engel- 
mann’s interest in the Yuccas began over 
fifty years ago, a time when but four 
species were generally recognized. Ex- 
plorers of the West and Southwest sent 
or brought to him many specimens of the 
genus — their leaves, flowers and fruits. 
These, however, did not clearly harmonize 
with such knowledge of the group as had 
previously been obtained and the greatest 
confusion existed as to the plants. The 
largest herbaria were notably poor in ma- 
terial. especially of fruits and seeds. Dr. 
Engelmann, in his studies and explorations 
species were indigenous, showed that both 
fruits and ripe seeds were produced abun- 
dantly. The scientist’s question, Why? 
appealed to him and he set about to solve 
the problem. From his knowledge of the 
process of pollenation he suspected this 
work was carried on by some insect native 
to the habitat of the Yuccas, but as yet not 
introduced into Europe with the plants. 
Careful observations on the flowers of Yuc- 
cas growing beneath the window of his St. 
Louis home were soon rewarded with suc- 
cess. All circumstantial evidence pointed 
to a tiny white moth as the object of his 
search ; a conclusion further substantiated 
by the discovery of the moth in the flow- 
ers of Yuccas growing in other and more 
remote parts of the city. Since Dr. Engel- 
mann was a botanist, he was interested 
chiefly in the plant side of the subject and 
at this point he turned the investigation of 
the insect over to Dr. C. V. Riley, then 
the State Entomologist of Missouri. To- 
gether they observed and worked till the 
beautiful story of two life-histories was J 
disclosed — one, of the plant ; the other, of 
the insect. Dr. Riley’s studies revealed , 
to him that the moth was so highly special- 
ized, more noticeable in the mouth parts 
and egg-laying device, as to be entirely dif- , 
ferent and distinct from any other moth of 1 
its near kindred that had previously been i 
described. Thereupon he gave to it the j 
technical name of Pronuba yuccasella, the 
“Yucca Pronuba,” or “Pronuba Moth.” 
The Yucca flower, as has been stated, is 
almost closed in the daytime and but few 
insects can enter it. Neither does it pro- 
duce nectar — the chief attraction to insects 
that commonly visit flowers. However, if j 
the partially closed flowers are examined 
during the day, many of them will dis- 
close the hiding places of a tiny white 
moth, or “miller,” scarcely more than half 
an inch long. It folds its wings together 
in roof- form over its back and rests 
lengthwise along one of the stamens. The 
whiteness of the insect blending with the 
white-walled floral chamber, all in diffused 
light, gives it ample protection, and indeed, 
one must frequently be very diligent in ^ 
his examination to be able to see it at all. 
| 
As dusk comes on and the flowers begin 
moths become very active, flitting about i 
from flower to flower and from plant to j 
plant. If, with a small “flashlight” or 
“bull’s-eye” lantern, one takes a position 1 
by a plant he will probably be able to see ' 
the moth climb one of the stamens and 
with its specially constructed mouth parts' 
scrape all the pollen from the anther and 1 
roll it into a small pellet. This is then 
carried to a second stamen and the pollen i 
from it is added to the pellet — the 
process being repeated from stamen to 
stamen until a good-sized Joall is formed. 
Then the insect changes its scene of opera- 
tion. Leaving the stamen, it goes to the 
pistil, which it explores very carefully, 1 
running around it and from top to bot- 
tom. When satisfied with the locality, it 
turns about till its head is toward the stig- 
matic, or upper end of the pistil; then it 
slowly backs downward between two 
stamens, feeling the surface of the ovary 
very carefully with the tip of its abdomen. 
When a suitable location is found, usually 
just below the middle of the pistil, it stops! 
the body movement and begins to drill 
with its ovipositor, or egg-depositing de- 
vice. This is long and sharp-pointed 
especially adapted for drilling a small 
deep hole into the heart of the pistil, when 
a single long, thread-like, transparent egg 
is deposited. As soon as this is accom ; 
plished the moth removes the ovipositor 
