THE EUROPEAN CORN BORER AND ITS CONTROL. 19 



terior of the stalk through the pedicel and into the ear; consequently, 

 the infested ears may not show external indications of injury. 



A combination of these larval habits may result in the presence of 

 several larva? within a single ear. In one instance a total of 15 were 

 found feeding on the interior and exterior of one ear. Extensive feeding 

 of this nature reduces the ear to a soft, decaying condition, totally unfit 

 for market, and unsuitable, even, for feeding to stock. This deteriora- 

 tion is hastened by the introduction of various rots and fungi, which 

 gain entrance to the plant through the holes made by the borers. Even 

 when only a single larva is present within the ear, its feeding renders the 

 ear unfit for market, while its use for seed, or for storage in cribs, is abso- 

 lutely prevented, owing to the softened condition of the kernels and their 

 tendency to quick decay. 



The percentage of ears infested in any given field depends upon the 

 degree of infestation. An actual field count, made in a one-eighth acre 

 plot of sweet corn located at West Medford, Mass., showed that, out of 

 a total of 3,311 ears present in this plot, the entire number were infested, 

 to a greater or lesser degree, by larvae of the borer. This plot was typical 

 of most of the fields and small garden patches of sweet corn found in the 

 territory where the pest has become well established. It serves as a 

 standard by which to judge the amount of damage to corn that may be 

 expected if the pest is not brought under control. 



Injury to the Leaf. 

 Newly hatched larvae of the European corn borer may feed upon the 

 upper or lower epidermis of the leaf blade before they enter the buds of 

 the tassel. This type of injury is of no economic importance, except 

 that it offers a possibility for poisoning the young larvae by application 

 of arsenicals. Partly grown larvae infrequently tunnel into the midrib 

 of the leaf blade, and also feed between the leaf sheath and the stalk. 



Summary of Injury to Corn. 

 The economic injury to corn may be summarized as follows: — 



1. Injury to tassel which results in poor fertilization. 



2. Injury to stalk which reduces vitality of plant. 



3. Injury to stalk which causes breaking over of plant. 



4. Injury to stalk which indirectly affects ear. 



5. Injury to ear which directly affects the yield. 



6. Injury to silk of ear which results in poor fertilization. 



Other Food Plants. 

 Dock. 

 In the absence of corn, dock is a common food plant of the first genera- 

 tion of European corn borer larvae. The plant is represented by at least 

 two different species in the area infested by P. nubilalis, and both species 



