THEIPS AS POLLINATORS OF BEET FLOWERS. 9 



Table III. — Pollination of beet flowers — experiments of June 26 and July 12, 1912. 



Experiment of June 26, 1912. 



Experiment of July 12, 1912. 





Description. 



Flow- 

 ers. 



Seeds. 



Spike. 



Description. l 



Flow- 

 ers. 



Seeds. 



Spike. 



. o3 

 J* 

 ft 



a 



o 



o5 



S 



^-5 



a 

 s> 



o 



s 



ft 



"ft 



o 



03 

 u 



m 



.a 



a 



3 



03 



o 



03 

 ft 



No.l 

 No. 2 



Thrips admitted 



do 



18 

 14 



6 



4 



12 

 10 



6C.66 

 71.14 



No.l 

 No. 2 

 No. 3 



Thrips admitted 



...do 



13 

 20 

 20 



8 

 17 

 20 



5 

 3 

 



38.46 

 15 





Totals 



Check 









32 



10 



22 



68.75 













1 Of the 33 flowers to which thrips were admitted in this experiment, 24.24 per cent are shown to have 

 been fertilized, while all the checks remained sterile. 



2 For entire set. 



CROSS-POLLINATION BY THRIPS. 



As already stated, other studies have shown that close pollination 

 of beets rarely results in fertilization and that self-fertilization does 

 not take place. To be of service to beets, thrips must therefore 

 bring about cross-pollination. The writer has found the impression 

 rather general that thrips do not travel from plant to plant to any 

 great extent. On this point the following evidence from the writer's 

 notes is available: 



July 19, 1912. — A great number of thrips had been shaken from seed beets in full 

 bloom into a large pan. In the slanting rays of the evening sun many of the adults, 

 which are winged, could be seen to fly from the collecting pan and alight on adjacent 

 plants. Their flight was sustained and fairly steady, though not nearly so rapid as 

 that of gnats. 



July 21, 1912. — Since attention was attracted to the flight of thrips, careful watch- 

 ing, when their wings glitter in the evening sunshine, revealed the fact that their 

 flight from plant to plant is voluntary and frequent; this flight is well sustained, 

 though very slow. They were seen to travel not only from one plant to the next, 

 4 feet away, but to more distant ones. The flight of many of these thrips was inter- 

 cepted by a sheet of white paper, upon which they alighted. Some of them were 

 chloroformed and examined. Pollen at this time was not very abundant, because 

 the plants were long past the time of maximum bloom. Counts were made showing 

 that 5 different thrips carried grains of pollen, as follows: No. 1, 5 grains; No. 2, 44 

 grains; No. 3, 3 grains; No. 4, 38 grains; No. 5, 4 grains. 



July 23, 1912. — An examination of the seed beets in plat 2, where seed is almost 

 ripe, showed an absence of thrips. The number of these insects on the plants now in 

 bloom in plat 1 is immense. [Plat 1 lies about 50 feet north of plat 2. Many beets 

 in plat 1 were planted later than those in plat 2 and were therefore still in bloom.] 

 Thrips were fairly numerous in plat 2 when the plants there were in bloom; therefore 

 it would appear that thrips migrate some distance in pursuit of pollen and nectar. 

 An examination of plants in plat 1, some of which had been planted earlier than 

 others, showed the earlier planted ones, now without bloom, to be devoid of thrips. 



This study established the fact that not only are thrips capable of 

 collecting and carrying pollen on their bodies and of effecting cross- 



