junei5, I9IS New Wheat Thrips 221 



smithii, Elymus canadense, E. virginicus, Syntherisma sanguinalis, Pani- 

 cum crus-galli, and Hordeum juhatum. They are found at all seasons of 

 the year on these grasses, but more especially during the interval between 

 harvest and wheat sowing. 



INJURY TO PLANTS 



The injury is confined to the leaves of young plants (PI. XXX, fig. 4), 

 unfolding heads and newly formed grains of wheat, and the young un- 

 folding leaves of some grasses. 



The method of feeding is similar to that of other allied species — that 

 is, by first puncturing and lacerating the tissues of the upper epidermis 

 of the leaf, or integument of the grain, then sucking out the juices. Both 

 larvae and adults feed in this manner, changing their point of attack 

 frequently, and thus in a short time a leaf or grain is literally covered with 

 lacerations. 



The leaves when attacked by a dozen or more individuals at one time 

 become badly mutilated in a few hours and, owing to the influence of 

 sunshine and \vind, soon acquire a "rusty" appearance. Since the in- 

 jured leaves nearly always cover the next unfolding leaf, the injury often 

 becomes disastrous to the plant by preventing the new shoot from devel- 

 oping. The heads are first attacked when in blossom, the pollen being 

 eaten greedily. The tender stamens and pistils are lacerated badly and 

 dry up very quickly, so that the embryo seeds are killed in a kind of 

 injury seldom observed and one wherein the damage can hardly be esti- 

 mated, although evidently it is considerable. As soon as the grains begin 

 to form, the thrips attack the husk, and later, gaining access to the husk, 

 they lacerate the tender integument of the newly forming grain. Grains 

 attacked at this stage are practically destroyed, and even after the milk 

 has become a dough the injury causes the grains to shrivel. 



The last portion of a wheat plant to ripen is the head, and therefore 

 the thrips remain on it until it becomes dry. They often stay on the 

 green heads until harvest, but leave the plants very soon after these 

 have been bound up into sheaves, afterwards subsisting on the common 

 grasses present in the fields. 



FIELD OBSERVATIONS 



The depredations of this tiny insect were first brought to the writer's 

 notice in the spring of 1908 at Pawnee, Okla., and Wellington, Kans. 

 Here they were first observed in abundance, doing much damage to the 

 new shoots of young growing wheat. With a few sweeps of the insect 

 net they were collected by the thousands from wheat plants throughout 

 April and May. In one instance where they were so very numerous the 

 crop was not worth harvesting, but the failure of the crop could not be 

 attributed entirely to the thrips, owing to the presence in abundance of 



