THRIPS AS POLLINATORS OF BEET FLOWERS. 3 



being exceedingly abundant in alfalfa blossoms. In Ogden the experi- 

 mental plats were located in the heart of a trucking district, where 

 many onions and other general truck crops are grown. At Jerome 

 the beet plats were surrounded by alfalfa fields. At Garland these 

 insects were fairly abundant. At Ogden in 1911 they were very 

 abundant. This may be better appreciated by a glance at Plate I, 

 which shows the thrips that were dislodged from the small branched 

 spike depicted in Plate II after the spike of flowers had been exposed 

 for a short time to the fumes of chloroform. 

 Before the thrips had recovered from anes- 

 thesia the spike and its branches were 

 distinctly outlined by the stupefied insects. 

 Notes taken at the time read as follows: 



August 7, 1912. — After treatment with chloroform, 85 

 thrips fell from a spike possessing 80 open flowers; from 

 another branched spike 190 thrips were dislodged. 



Inspection of beet flowers sometimes re- 

 vealed as many as five or six thrips in a 

 single perianth. 



In 1912, on the site of an old Chinese truck 

 garden at Odgen, thrips became extraordi- 

 narily numerous during the late blooming 

 period, when they fairly swarmed in and 

 about the beet flowers. It was then as- 

 certained that in addition to drinking the nectar and devouring the 

 pollen they 'may also injure the floral organs. 



Earlier studies of the injurious effects of various sucking insects, 

 including aphides, red spiders, and thrips, on sugar beets, had estab- 

 lished the fact that the last-named insects sustain their unenviable 

 character on sugar beets also; they cause on young sugar beets a 

 great diversity of leaf curls and distortions. On the spikes and bract- 

 lets of seed beets small silvery scars may be found as a result of their 

 attacks. The thrips is more destructive than most sucking insects, 

 because, not satisfied with merely puncturing, it tears and grubs up 

 the surface tissues of its food plants with its powerful mouth cones, or 

 proboscis (fig. 2), in order to release a more copious flow of the plant 

 juices. 1 It reminds one of the actions of a hog. 



These studies were extended to the observation of thrips on the 

 inflorescence of sugar beets. The spikes and spikelets of the sugar 

 beet, with their closely arranged spirals of flower clusters, are very 

 numerous and afford excellent hiding places for these insects. It 

 was found that as the period of most abundant bloom approached, 

 thrips became increasingly numerous, partly through migration from 



Fig. 2.— Side view of the head of 

 a thrips, showing the mouth 

 parts. Much enlarged. (After 

 Moulton.) 



1 Moulton, Dudley. The pear thrips and its control. United States Department of Agriculture, Bureau 

 of Entomology, Bulletin 80, pt. 4, p. 54, 1912. 



