4 



BULLETIN" 104, U. S. DEPARTMENT OF AGRICULTURE. 



other plants, but more especially through breeding. Eggs are 

 deposited and hatched on the spikes themselves. On hatching, the 

 young larvae quickly seek the flowers, doubtless attracted by the 

 pungent fragrance of the nectar, and literally wallow in the nectar 

 and pollen, avidly drinking the one and voraciously devouring the 

 other. 



Observations covering five seasons have shown that several species 

 of Thysanoptera visit beet flowers and that the number of individuals 

 varies greatly with the locality and general environments, notably 

 with the crops in the vicinity. At Jerome, Idaho, in 1913, on land only 

 recently cleared from sagebrush, thrips were rather scarce, although 



somewhat abundant in alfalfa in near-by 

 fields. These insects have also been seen in 

 moderate abundance on seed beets in Indiana 

 and Michigan. 



THRIPS AS POLLEN BEARERS. 



The writer has been able to discover in the 

 literature very little reference to thrips as a 

 pollen bearer and no proof of its ability to 

 bring about the fertilization of flowers. 



Darwin was familiar with the visits of thrips 

 and kept hi mind the possibility 'that they 

 might gam entrance through his nets. 



Hermann Miiller 1 records their occurrence 

 in the flowers of several genera and species, 

 but does not mention beets. In a paragraph 

 on Thysanoptera he says that "probably few 

 flowers, if any, are altogether exempt from 

 their visits, and though they have seldom been 

 detected in the conveyance of pollen, yet from 

 their great abundance, their value as fertilizers 

 must not be overlooked. It is almost im- 

 possible to exclude these tiny insects by means of nets. The Thysan- 

 optera seek both pollen and honey. They seize a single pollen grain 

 in their mandibles and convey it to the mouth." 



Uzel, 2 in Bohemia, has noted the visits of several species of Thy- 

 sanoptera among sugar and stock beets, but adduces no evidence in 

 proof of the actual pollination of those flowers by thrips. 



On August 3, 1911, at the experimental plats in Ogden, Utah, 

 spikes of beet flowers were exposed to the fumes of chloroform to 



i Miiller, Hermann. The fertilisation of flowers. Tr. and ed. by D'Arcy W. Thompson, London, 18S3, 

 p. 44-15. 



2 Uzel, Heinrich. Uber die Insekten, welche die Bliiten der Zucker- irnd Futterrube besuchen. Zeit- 

 schriftfiir Zuckerindustrie in Bohmen, Jahrg. 37, p. 1S2-197, 1913. 



Fig. 3. — Larva of Thrips tabaci 

 (second stage) taken from a 

 sugar-beet flower. The insect 

 carries numerous beet-pollen 

 grains on its body. X 50. 

 (Sketch of the larva after Rus- 

 sell.) 



