BULLET 



it 



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 sn all, 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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