222 Journal of Agricultural Research voi.iv, no. 3 



both the Hessian fly (Mayetiola destructor Say) and the chinch bug 

 {Blissus leticopterus Say). 



The thrips again appeared in the spring of 1909 in considerable num- 

 bers, but not enough to cause noticeable injury. In April and May 

 many eggs and larv^se were killed by the hot sun and wind, on account 

 of the drying of the wheat leaves. However, some of them thrived and 

 reproduced freely, for in August, when volunteer plants sprouted, they 

 occurred in large numbers and continued to reproduce and feed on the 

 fall-sown crops until hibernation. 



The winter of 1909-10 was very severe, and only a small number of 

 this species survived; consequently, but few were found during the year 

 1 910 and a still smaller number were noted in 191 1 and 191 2. 



In the late fall of 1912 females were found in clumps of Agropyron 

 smiihii and also a number were in stools of wheat, in which they hiber- 

 nated. Thrips were common on wheat and grasses during the growing 

 season of 191 3, hibernating in the late fall and appearing in swarms on 

 young wheat in early March, 1914. By the ist of April the larvae, now 

 nearly grown, were cutting the shoots severely. They ceased feeding 

 about the third week of April and pupated. By the time the adults 

 were ready to issue, the wheat plants had outgrown all previous injury. 

 Favorable rains produced a rapid growth of wheat, which apparently 

 did not interfere with oviposition or Avith the feeding of the young thrips 

 larvae. By the middle of May, when the w^heat was heading, the second 

 brood of larvae readily infested-the young heads, feeding upon the stamens, 

 pollen, and pistils, and later attacking the integument of the grain. Larvae 

 and adult thrips continued to feed on the heads until the crop was 

 harvested, very few being dislodged by the binder. Subsequently they 

 clung to the heads for three or four days, finally leaving the grain for 

 grasses or entering the soil for pupation. 



Neither adults nor larvae could be found in stubble fields during the 

 summer, but as soon as volunteer wheat plants pushed up in early Sep- 

 tember the thrips were found in all parts of the field, which would indicate 

 that they had been present all the time. As no evidence of thrips was 

 found in the fields during the summer, it follows that the pupae had 

 waited for the rains, the moisture being sufficient to sprout wheat grains 

 and also to cause the adults to issue. 



The thrips did no appreciable injury to young plants in the fall of 

 1914, but in early December of that year many were hibernating in the 

 principal host plants, the stools of wheat and clumps of Agropyron 

 smiihii. 



HIBERNATION 



The adults and larvae hibernated in clumps of wheat, Andropogon 

 scoparius, and other grasses in the fall of 1909. Although living adults 

 and larvae were found in wheat on February 8, 1910, and again on March i, 



