No. 567] BIOLOGY OF THE THYSANOPTERA 



163 



Facts to be Explained 



The following are some of the facts of habits and dis- 

 tribution of the more abundant species for which physio- 

 logical explanations were sought. Some of these facts 

 are stated in my former paper, some of them doubtless 

 the common property of all thysanopterists; others, so 

 far as I know, have never been recorded. 



Eutlirips tritici is found almost exclusively in situa- 

 tions where it is concealed, as among the florets of com- 

 posite flowers, in clusters of young leaves, or in almost 

 any close crevice where the tissues are not too hard or 

 tough to be pierced. It appears to make little difference 

 what species of plant is inhabited, provided a concealed 

 situation is available. In the paper cited above (Shull, 

 1911) I gave a list of seventy species of plant on which 

 Eutlirips tritici was taken, and I have since collected it on 

 a number of plants not included in that list. But with 

 rare exceptions, it has been found in crevices where it was 

 not readily visible. In related plants, it is always more 

 abundant in those affording concealed situations. Thus, 

 in white clover (Tri folium repens) and in red clover 

 {T. pratense), this thrips is usually abundant; while on 

 the related yellow, and white, sweet clovers (Melilotus 

 officinalis and M. alba, respectively), growing along with 

 the red and white clovers, Eutlirips tritici is usually rare 

 or wanting. The flowers of Melilotus are widely sepa- 

 rated from one another on the stem, and do not afford 

 concealment (Shull, 1911). 



If, while Eutlirips is in one of these crevices, it is dis- 

 turbed, as by gently rubbing or pressing the flower, it 

 quickly comes out of its retreat and crawls rapidly away, 

 or takes to flight. The larvae show the same behavior as 

 the adults in this regard, except, of course, that they do 

 not fly. 



Anaphothrips striatus is found usually on grasses of 

 various kinds, rarely on leaves of other plants. The spe- 

 cies of grass seems to make little difference. Some indi- 

 viduals are found in perfectly exposed situations, as on 



