THEIPS AS POLLINATORS OF BEET FLOWERS. 11 



they actually do effect pollination and fertilization after passing 

 through such covers. 



The following is an instance of what might be expected to occur 

 through the agency of thrips: The horticulturist of a well-known 

 firm of seedsmen in the United States noted that his asters became 

 fertilized although covered with cloth bags. The writer suggested 

 that thrips might be responsible for this. The horticulturist replied 

 in part that "the aster flowers were merely covered with coarse- 

 meshed cloth to see if they were self-fertile. Insects as small as 

 thrips would not have been excluded. We merely learned that the 

 fertilization of asters is not dependent on the insects — mostly 

 beetles — that one ordinarily sees on the flowers." 



The horticulturist and plant breeder may not disregard these 

 insects. They introduce an element of uncertainty to be guarded 

 against with the utmost care and circumspection. Their minute size, 

 inconspicuous color, great numbers, and the fact that they are almost 

 ubiquitous make them a factor to be reckoned with by every worker 

 along these lines and necessitate the development of special precau- 

 tions and technic. 



Covers of net, cloth, and sheeting afford no real protection against 

 them; even paper bags must be applied with great care. The writer 

 found the method described and illustrated in connection with these 

 experiments to be simple and efficacious. 



It is as necessary to rid the isolated portion of plant and flower of 

 thrips already present as; to prevent the access of others after isola- 

 tion. In these experiments the practice was made of carefully scru- 

 tinizing each spike of buds or flowers before covering it and brushing 

 off any thrips that might be present with a camel's-hair or sable 

 brush, sometimes also spraying the spike thoroughly with water. In 

 the summer of 1912 the use of nicotine sulphate also was tried, as 

 shown in the folio whig notes : 



July 24, 1912. — At this late blooming period, thrips have become exceedingly 

 numerous on all spikes in bloom; they interfere seriously with pollination work. 

 To ascertain whether a simple, practical method might be available to rid the individ- 

 ual spikes completely of these pests, the following experiment was carried out: Some 

 spikes, badly infested with thrips, were selected. Before operating on the spikes, 

 they were immersed in the following solution: Water, 2 pints; nicofume (nicotine 

 sulphate), 1 tablespoonful. 



Spikes 1, 2, and 3 (in their normal condition, i. e., bearing flowers of all stages — 

 buds, flowers just opening, and flowers already fertilized) were immersed in the above 

 solution 10 seconds; then they were at once isolated with manila paper bags in the 

 manner previously described. 



Spike 4, with selected buds emasculated, was treated with nicofume like the pre- 

 ceding, bagged, and (when stigmata had become receptive) pollinated. 



Spikes 5 and 6 were treated like No. 4, but not pollinated. 



Spike 7 was merely shaken and flowers blown upon to dislodge thrips; flowers 

 emasculated. 



