February, ’24] 
caffrey: corn borer research 
115 
have been found in approximately 20 species of plants other than com. 
During the past season two fields of broom corn in western New York 
showed stalk infestations of 12.7% and 15.8% respectively. 
Indirect Injury to Corn 
During the progress of making examinations of corn to determine the 
amount of injury caused by P. nubilalis, it has become apparent that 
the actual reduction in yield through injury to the stalk and ear-stem, 
is usually the most important damage caused by the corn borer, in the 
instance of medium or heavy infestation at least. 
It has been found quite difficult to accurately estimate the degree of 
this indirect injury, but during the summer of 1923 a special attempt 
was made to obtain information upon this point by protecting from 
infestation a block of 16 hills of Longfellow flint field corn plants which 
were situated in the center of a large plot of the same variety. From 
its location and the time of planting, it was expected that this entire 
plot would be subjected to severe injury. Egg clusters and migrant 
larvae were carefully removed at frequent intervals from the protected 
block of plants and additional protection from migrating larvae was se¬ 
cured by surrounding the protected plants with a barrier coated with 
sticky material. It proved to be impossible to entirely protect the 
plants under observation, but at harvest time these plants contained, 
on an average, less than one-third the number of larvae per plant than 
the plants in the remainder of the plot, and a comparison of the weight 
of the ears from the protected and unprotected plants showed an 
apparent reduction in weight of approximately 30% in the ears from the 
unprotected plants. 
Computations in the field to determine the importance of indirect 
injury, have uniformly shown an important loss from this source, but a 
really saitsfactory and accurate method of computation has not yet 
been worked out. During the past season examinations which were 
made in two fields of field com in New England, indicated losses in 
weight of ears of 20% and 8% respectively, due apparently to indirect 
injury. About 45% and 50% of the plants were infested in each field. 
Similar examinations in two fields of sweet corn, representing a stalk 
infestation of approximately 50%, indicated an apparent loss due to 
indirect injury of 18% of the ears, as compared to non-infested plants, 
and an increase of 31% in number of nubbins. 
Insecticides 
In an attempt to develop an insecticide that could be used to prevent 
