^ THYSANOPTERA AND ORTHOPTERA. IPo 



care was taken to select flowers of approximately the same size and age, 

 to have them equally abundant, etc., as in the previous counts (Table 

 I). The road was a well traveled Rural Free Delivery route and ran 

 north and south; the flower examined was white clover (Trifolmrn 

 repens) ; and the thrips, as l^efore, were chiefly Euthrips tritici. The 

 results are given in Table II. 



TABLE II. — Showing the number of thrip.s taken from G lieads of white 

 clover (Trifolium repens) at different distances from a highway. 



Number of thrips in six heads of clover. Distance from the road in feet. 



92 4 



81 8 



46 20 



35 40 



39 80 



35 165 



45 240 



48 320 



34 400 



The figures seem to show that the decrease in numbers in passing 

 from the road is all in the first 40 feet, or perhaps even in the first 20 

 feet. 



Tendency not to migrate. If this tendency to remain crowded in one 

 place rather than fly away is as marked as the figures seem to show, it 

 ought to be capable of demonstration in the laboratory. With this 

 point in view, tw^o heads of Canada thistle {Cirsium arvense) were 

 brought in and placed in water. One, in its prime, or perhaps slightly 

 past, was from a bunch which averaged more than 75 thrips per flower, 

 and seemed as badly infested as the others. The other was an opening 

 biid in which the tips of the bracts had separated so as to expose the 

 tips of the florets, but none of the florets were open, and I could find no 

 thrips among them. The l^ud and the flower were placed about 3 cm. 

 apart. The leaves immediately below them touched so that migrat- 

 ing thrips could crawl, as well as fly, to the opening flower. At the end 

 of 24 hours the l)ud had nearly all its florets open, but contained no 

 thrips; the older flower was decidedly Ijrownish already, but apparently 



