140 
more quickly and completely than earlier sown, unpastured fields. 
But it must be remembered that here the almost universal destruc- 
tion was caused principally by Toxoptera drifting in from outside 
sources. 
One feature of attack by Toxoptera has been especially noticeable 
throughout most portions of the country seriously ravaged by the 
pest, particularly where only wingless viviparous females have been 
found. In such fields the destruction was confined to circular areas 
which constantly increased in size as the season advanced, so long as 
meteorological conditions favorable to the increase of the pest pre- 
vailed; unless, in the meantime, the entire field had become overrun 
from the swarms drifting in from without. The occurrence of these 
spots (see Plate I, fig. 2) in the fields, while general, is not universal. 
For instance, the senior author did not observe them in the fields of 
fall-sown oats in South Carolina, in April, 1907, but he did find them 
about Winston-Salem, N. C, a day or two later. At Summers, 
Ark., Mr. C. N. Ainslie, observed a field of wheat, March 18, 1907, 
where a rectangular strip at one end had been totally killed out by 
Toxoptera, and learned from the owner that this area exactly corre- 
sponded with that of a small patch of oats which the previous year 
had failed to produce more than a very poor crop and had been 
plowed under without cutting. In preparing the ground for wheat 
in the fall of 1906, a volunteer growth of oats was reported to have 
sprung up on this area after plowing. Again the same observer, a 
little later in the season, found that the regularity of the occurrence 
of these spots in rows across a field, in northern Oklahoma, exactly 
corresponded to the location in this same field the previous summer 
of oat shocks, which had been allowed to stand out through a period 
of wet weather; the volunteer grain having sprung up there later in 
the season and remained growing amongst the young wheat in the 
fall. In Texas the relation of this volunteer growth in the fields, 
in autumn and early winter, to the abundance of Toxoptera does not 
appear to differ materially from what is known to occur elsewhere. 
When the secretary of the Texas Grain Dealers' Association first 
appealed to the Government for aid in investigating the pest, particu- 
lar attention was directed to the possibility that methods might be 
devised for its control by spraying or otherwise treating the spots in 
grain fields, for the purpose of checking its ravages before these 
infested spots had increased in size and before the pest had spread 
from them over the entire field. 
Thus it will be seen that primarily infestation is first invited by 
the volunteer growth starting up in cultivated fields in autumn. 
If such fields are sown to wheat or oats in the fall, the pest spreads 
from this earlier growth to the younger and more tender grain. This 
will of itself suggest several entirely practical cultural methods likely to 
restrict and prevent the development of the pest in the fields in autumn. 
