140 THE SPBI2CG GEAI^-APHIS OR ' k GEEEX BUG. 





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 eonstantlv 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. X. C. a day or two later. At Summers, 

 Ark., Mr. C. X. Ainslie, observed a field of wheat, March IS, 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 Dealer-" 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 fur 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 soggiest several entirely practical cultural methods likely to 

 restrict and prevent the development of the pest in the fields in autumn. 



