

THE GRASS THRIPS. 



WARREX E. HINDS, B.S. 



Introduction. 



The Thysanoptera form a group of insects whicb, on account 

 of their small size and apparent insignificance, have been much 

 neglected by entomologists. Their position with reference to other 

 groups has accordingly been doubtful, and at various times they 

 have been assigned a place in no less than three different orders. 

 Linnjfius considered thrips as having affinities with the Hemiptera, 

 and placed them in a genus immediately following his genus Coccus. 

 While some of the followers of Linnoeus retained them in this posi- 

 tion, others referred them to the Orthoptera and still others to 

 the Pseudoneuroptera. More recently, however, they have been 

 placed in an order by themselves, to which the names Thysanoptera 

 and Physopoda (Physapoda) have been given ; but, as the former 

 has priority, it should be adopted. 



Although these insects are widely distributed and extremely 

 abundant, being found in profusion in very many flowers, less than 

 one hundred and fifty species have been described, of which about 

 one hundred and twenty are from Europe and less than twenty 

 from the United States. They range in size from one-fiftieth to 

 one-third of an inch in length, the latter size having thus far been 

 found only in Australian species. Undoubtedly the difficulties en- 

 countered in studying and accurately interpreting the mouth parts 

 of such small animals have had much to do with the confusion re- 

 garding the systematic position of this group of insects. 



Their mouth parts (Plate III., figs. 19, 20, 21 and 22) are inter- 

 mediate in form between those of sucking and of chewing insects, 

 but they probably take their food by suction. The mouth parts 

 and other structures of the head are in part asymmetrical, a fact 

 of considerable interest, as is also the location of the stigmata 

 (Plate I., figs. 1 and 3). These are situated in adults upon the 

 anterior angle of each side of the mesothorax and on each side of 

 the first and eighth abdominal segments. A fourth pair, which is 

 less conspicuous, is found upon the mctathorax behind the place 

 of attachment of the hind wings. In the larvne the abdominal 

 stigmata are found upon the second and eighth segments. 



