BULLETIN OF THE 
No. 104 
Contribution from the Bureau of Plant Industry, Wm. A. Taylor, Chief 
July 10, 1914. 
THRIPS AS POLLINATORS OF BEET FLOWERS. 
By Harry B. Shaw, 
Assistant Pathologist, Office of Cotton and Truck Diseases and Sugar-Plant Investigations. 
INTRODUCTION. 
While conducting breeding experiments with sugar beets during a 
period of more than five years, it could never be observed that the 
beet flower, despite the pungent fragrance of its nectar and the 
remarkable abundance of its pollen, attracted nearly as many insect 
visitors as numerous blooms offering less pronounced attractions. 
Especially significant was the rarity of the visits of the honeybee 
and other common species of Hymenoptera. It appeared as though 
nature had vainly provided powerful insect lures, excepting only 
those of conspicuous size and color. It is true that insects, some of 
them capable of transferring pollen from flower to flower, do visit 
beet flowers, but relatively their numbers are small and their visits 
few. 
These breeding experiments necessitated the isolation and hand 
pollination of numerous beet flowers. Not infrequently, in spite of 
careful technic, it was found that single flowers which had been 
emasculated and protected by paper bags from pollination became 
fertilized and produced seed in a manner at the time inexplicable. 
Although the actual percentage of such cases was small, it was 
sufficient to attract attention and to cast doubt upon the thorough- 
ness of the protection afforded by the bags. Not only is the beet 
flower protandrous, but numerous attempts of the writer to effect 
close fertilization by preserving the pollen until the stigma of the 
same flower should become receptive, then applying the pollen, have 
failed. The above-mentioned fertilization, therefore, could not have 
been accomplished by pollen from any one of the single flowers 
operated on, even had such pollen reached the stigma; in other 
words, the beet flower can not be self-fertilized. The most probable 
explanation for the fertilization of these isolated flowers was the 
Note.— The investigations and experiments reported in this bulletin are of interest to horticulturists and 
plant breeders. 
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