90 JOrRN.\L OF ECONOMIC ENTOMOLOGY [Vol. 14 



to estimate the actual loss since much of the injury is obscure and often 

 attributed to other factors. During the past five years, several distinct 

 lines of investigational work have been under way. The present paper, 

 howxver, is limited to a discussion of the more important types of injury 

 and to certain experiments indicating possible means for the reduction 

 of the injury. 



Injury to Corn 



In the case of com, all parts of the plant above ground are subject to 

 injury, although the greatest damage occurs to the tassel. The aphids 

 usually appear on corn during the last of June or the first of July, and are 

 to be found deep in the curl feeding on the tenderer parts of the leaves. 

 As the tassel develops in the curl, these insects forsake the leaves, con- 

 centrating on the tassel and especially on the central branch, resulting 

 in several types of injury. The entire tassel may become so heavily 

 infested that it fails to function (Plate 2, fig. 1). This type of injury 

 was rather common in 1919, amounting to 10 per cent, of the plants 

 in many of the fields about Manhattan. A more common form of 

 damage, however, is caused by the concentration of the aphids in the 

 central branch and a few adjacent branches of the tassel where they 

 prevent the shedding of pollen by sapping the juices and gumming the 

 spikelets with honey dew (Plate 2, fig. 3a). In 1920, in the vicinity of 

 Manhattan, approximately 50 percent, of the com plants exhibited this 

 type of injury to such an extent that no pollen was shed. This meant a 

 loss of from 15 to 20 percent, of the pollen, and since the central branch 

 is the first to shed pollen, this is an important item. The com crop of 

 Kansas is often dependent on the early pollination of the silks, since the 

 hot winds and dry weather of midsummer may be fatal to both tassels 

 and silks. In addition, the emergence of the tassel may be delayed 

 or it may not fully emerge from the boot, in either case resulting in a loss 

 of pollen. Plate 2, figure 2, shows a plant whose tassel has not fully 

 emerged from the boot, while plate 3, figure 4 shows a normal tassel. 

 In the case where the tassel does not fully emerge, much of the pollen 

 is caught in the axils of the leaves where it offers an ideal medium for the 

 development of molds and rots, frequently resulting in the entire loss 

 of the top. These growths often extend down the stalks (Plate 3, fig. 5), 

 producing a weakened condition which is detrimental to the developing 

 ear. As a rule the leaves show little injury, but in cases of severe infesta- 

 tion they may become yellow and occasionally die. During the past two 

 years very little direct injury to "the ears has been noted. In a few cases 

 aphids were found in large numbers on ears when they were feeding on 

 the silks and the soft grains. As a result, maturity was hastened and 

 the ears were small and poorly filled. 



