THRIPS AS POLLINATORS OF BEET FLOWERS. 



dislodge insects that might be harboring in them. As already stated, 

 thrips in unsuspected number were thus removed. (Pis. I and II.) 

 A microscopic examination of many of these — larva? and adults — 

 showed that without exception beet pollen grains were present on 

 their bodies (fig. 3). 



The original notes under this date are as follows: 



August 3, 1911. — Discovered that Thrips sp. [later determined as Thrips tabaci] are 

 exceedingly numerous on and among beet flowers. Some spikes were collected, and 

 absorbent cotton sprinkled with chloroform was held over them to stupefy any insects 

 that might be present. Thrips fell off and were microscopically examined. Without 

 exception, each bore among its body hairs numerous sugar-beet pollen grains. Some 

 open flowers were then examined, and thrips, as they recovered from their stupor, were 

 observed to enter the perianth, where they moved about quite actively, traveling over 

 every part. Many pollen grains were picked up by the insects' body hairs, others 

 were dropped; pollen was also transferred from one insect to another when they came 

 in contact one with another. 



Almost at the close of the blooming period of beets, counts were 

 made of the pollen grains borne by a number of thrips dislodged with 

 chloroform from beet spikes, as shown in Table I. 



Table I. — Beet pollen grains on thrips, near the close of the blooming period. 



Stage of development of the insect. 



Number of grains found on 

 surface indicated. 



Dorsal. 



Abdomi- 

 nal. 



Total. 





30 

 02 

 53 



10 



78 

 82 



40 



Adult : 



140 



Do 



135 







These pollen grains were distributed over every part of their bodies, 

 even along the antennas. Nor do these figures represent unusual 

 individuals. The blooming period was practically over at this time; 

 pollen was therefore not very abundant. Both larval and adult 

 thrips have since been seen to be literally covered with beet pollen. 



EXPERIMENTS IN THE POLLINATION OF BEET FLOWERS. 



The foregoing results were both interesting and surprising, and at 

 once suggested, among others, the following queries : 



(1) Do the thrips in this instance redeem themselves from their hitherto wholly 

 evil reputation by playing an essential, or even an important, role in the fertilization 

 of beet flowers? Or, do they simply convey pollen from one flower to another on 

 the same plant and thus effect close pollination only? 1 



i Other experiments have shown close pollination of beet flowers to be almost absolutely ineffective in 

 bringing about fertilization, which is undesirable even when successful. Self-fertilization is not possible. 

 The term "self-fertilization" is here used to mean that resulting from the pollen of the same flower; "close 

 pollination," or "close fertilization," that effected by the application of pollen from one flower to another 

 on the same plant; " cross-pollination," that between any two plants. 



