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THE AMERICAN NATURALIST [Vol. XLVIII 



the dying of their food plants ; but the greater proportion 

 of males throughout August is probably significant. It 

 should also be stated that I have collected adults of this 

 species, of both sexes, from dead mullein spikes in late 

 winter. 



Anthothrips niger was found only in the female sex. 

 There are no records of males of this species, so far as I 

 am aware, in any published work. 



Thrips tabaci was taken almost exclusively in the 

 female sex, the two males found September 2 being the 

 only ones I have ever collected. 



In Anaphothrips striatus the total number of males is 

 less than 25 per cent. On August 20 and September 2 the 

 proportion of males is considerably greater than 25 per 

 cent., especially on the former date, while at other times 

 the proportion was nearly always less. The collection on 

 August 20 can hardly have been erroneous by chance, for 

 the figures given for that date are combined figures for 

 two collections from different localities. In one of these 

 collections there were 13 females and 14 males, in the 

 other 26 females and 34 males. This strengthens the 

 probability that the excess of males is significant. 



Thrips physopus was collected in small numbers, but 

 shows a fairly constant proportion of males. 



Chirothrips manicatus presents curious phenomena. 

 All the collections up to the end of July were made on 

 timothy heads in a small patch a few feet square near the 

 laboratory. On July 11 careful search revealed numer- 

 ous females, but only one male. By July 19 almost all 

 the thrips of this species were gone; only 5 specimens 

 were obtained, and these were females. Less than two 

 weeks later, however (July 30), on other timothy heads 

 in the same small patch, there were found 51 males and 

 but 1 female. No living thrips were taken here later, as 

 the timothy died; but subsequent collections elsewhere, 

 from timothy and bluegrass, show again almost ex- 

 clusively males. 



