Thrips 



considerable damage by injury to the essential organs of flowers. 

 Although the statement has been made that they sometimes feed 

 upon other insects, the evidence is not good. An interesting 

 <brm in this country lives in the sheaths of timothy grass and 

 sometimes causes the dying of the heads of the grass. Some- 

 times they are found under bark and in fungi, and in Australia some 

 of them form galls on the leaves of acacias. In the United States, 

 however, they are most abundantly found in flowers and fre- 

 quently in the heads of wheat. In greenhouses thrips are 

 especially noticeable. Dracaenas are said to suffer especially from 

 their attacks. They are commonly found on chrysanthemums, 

 on hydrangias, in orange blossoms, and many other flowers. 

 Probably the most injurious species in this country, however, is 

 the so-called onion thrips which causes the disease known as the 

 white blast of onions. The same species is found on leaves of 

 cabbage and cauliflower, squash, turnips, nasturtiums, and many 

 other plants. It is also found in Europe where it occurs on 

 tobacco as well as upon garden plants. It is known as Thrips 

 tabaci Lind. 



It does not seem to be generally known that parthenogensis 

 has been found to occur with thrips. Less than one hundred and 

 fifty species are known, but almost no one has taken the trouble 

 to collect these little creatures in out-of-the-way places, and it is 

 reasonable to suppose that the order will be found to be quite 

 numerous in species. 



3*9 



