ANNUAL REPORT, 1937 63 



frequent rains interrupted the 5-day schedule and often occurred soon after the 

 materials were applied. At least twice it was necessary to make a reapplication 

 following the rain so that 5 applications of sprays and 6 of the dust were made. 



There was considerable difference in the infestation on the three farms. In the 

 plot dusted with dual-fixed nicotine, 6 percent of the treated plants and 36 per- 

 cent of the checks showed stalk infestation. In the derris plot, 5 percent of the 

 sprayed and 12 percent of the checks were damaged by borers. In the treated 

 plots the infested stalks were not often seriously damaged and for the most part 

 they contained only 1 or 2 small, young stage larvae, whereas in the checks t he- 

 stalks were badly riddled, often contained from 5 to 8 mature borers, and in many 

 cases had broken down before the ears had fully matured. The loss of vitality 

 to the plants caused by even a light or moderate infestation is clearly reflected 

 in the yield records as shown by the following table. 



Increase of Treated over Untreated 

 Percentage Plots 



Material of ■ ■ — • 



■ Infestation Increase in ' . Increase in 



Total Ears Uninfested Ears 



per Acre per Acre 



Dual-fixed nicotine (dust) 30 225 1562 



Derris (spray) 5 ' 1692 2052 



In every case the treated plots showed an increased total yield over the checks. 

 On the basis of uninfested ears, the difference was even more pronounced. Even 

 in the case of a comparatively light infestation as in the derris plots, an advantage 

 of more than 2,000 ears per acre represented a considerable profit to the grower. 



A more significant index of the value of the treatments is the relatjflfe proportion 

 of Grade 1 corn harvested from the experimental plots as shown in the following 

 table. 



Material Percentage of Total Yield 



Uninfested Grade 1 ears 



Dusted Plots Check Plots Dusted Plots Check Plots 



Dual-fixed nicotine 92.8 70 76 48 



Nicotine tannate 97.6 94.4 72 60 



Derris 98.3 94.9 88 81 



The field containing the derris plots was heavily fertilized. The corn made 

 excessive stalk growth and many of the ears did not fully develop and were graded 

 as culls. Since the total yield in this field, however, was at the rate of 24,000 ears 

 per acre, even the small difference of 7 percent represented an increase of 1,680 

 ears. 



Since the growers could guarantee borer-free ears, they found a steady demand 

 for their corn and disposed of the crop at a premium. So few of the ears in the 

 treated plots were infested that the growers were able to eliminate the expense of 

 time and labor ordinarily necessary to examine each ear for borers, thus making 

 a material reduction in their marketing costs. 



Insects Concerned in the Dispersal of Dutch Elm Disease. (W. B. Becker.) 

 Research work on the biology of the native elm bark beetle, Hylurgopinus rufipes 

 . Eich., was continued. Freshly cut American elm logs in which eggs were laid 

 in the fall of 1936 and in which the insects passed the winter as larvae were 

 again attacked by new adults in the spring of 1937 for oviposition purposes. 

 Some slight emergence began from these logs early in July and kept up at a very 

 low rate until early in August when the daily emergence increased considerably. 

 At that same time emergence started from logs which had been cut in the early 



