-6o4- 
serious sacrifice in the adequateness of the data obtained. With the exception of 
the counties surveyed in Indiana and Maine, 10 cornfields distributed at random 
were examined in each county included. in the program, the sampling in each field 
consisting of a count of infestation in 25 consecutive plants taken a short dis- 
tance into the field from near the middle of its most accessible edge, and the 
dissection of the first 2 plants found infested to -determine the number of borers 
per infested plant. In Indiana and Maine, where an average of 20 to 25 cornfield? 
were taken at random within each county, the population figure for each field was 
based on the examination of 100 plants (25 consecutive plants in the approximate 
center of each quarter of the field) and the' dissection of either 5 or 10 infested 
plants. In either procedure, the product of the percentage of plant infestation 
in a field and the average number of borers per infested plant provided a figure 
designated as the average number of borers per 100 plants. The population aver- 
ages derived in this wav for the individual fields were then grouped in the cal- 
culation of county averages. 
In the 1939 survey a total of 3.^89 cornfields were examined in 285 countie? 
of l6 States infested by the European cofn bor ;r. Two small counties were com- 
bined in each of 2 States and each pair treated as a single county. The number 
of counties surveyed and the resultant average number of borers per 100 plants 
in each State, and in the entire an a, are given in table 1, In. an alphabetical 
arrangement by States and the counties surveyed within each of them, the data on 
average number of borers per 100 plants in 1939 are presented in table 2, togethej 
with comparable figures obtained in 1938 and in certain other years when more or 
less extensive surveys were conducted by the Bureau. Definite comparisons of the 
abundance of the. corn borer in 1939 and 1938 are possible only for those counties 
or county groups surveyed in these 2 y’ars, and on this basis the status of the 
insect in 1939. as compared with 1938, is shown on map 1, The relative abundance 
of the corn borer over the entire area surveyed in 1939 is illustrated on map 2 f 
In reading the data given in the tables it should be noted that a zero recorded 
for any county merely indicates a population so low that no infested pi, ants 
occurred within the counts made and does not moan the complete absence of the 
borer. The following discussion summarizes the more important features of the 
survey data. 
The greatest abundance of the European corn borer in the United States in 
the fall of 1939 was found in southern New England, where 5 counties in eastern 
Massachusetts, 2 in central and 2 in eastern Connecticut, and 4 in Rhode Island 
averaged 501-900 borers per 100 plants, and in th« tip of the "thumb” section of 
Where 1 county had a lDorer population of this. size. .Populations of 
IOI-500 borers per 100 plants appeared in 4 counties in central and 1 in south- 
as em Massachusetts, 2 in western and 2 in central Connecticut, 2 in south- 
eastern New Hampshire, 1 in southeastern and 2 in northwestern Vermont 1 in 
wstorn and 5 in eastern Hen Jfork and 2 on long Inland, 3 In northeastern and 1 
kJv 1 ? 1 No ” u f er!,e y, 1 in southeastern Fennr.--lvan.la, 1 in northeastern and l4 ir 
remainder°nf Jv* 0 ; 5 9astern ™ a 15 in southeastern Michigan. In the 
covered territ °g surveyed in 1939, comprising 209 of the 235 counties 
covered, the average number of borers per 100 pi, ants in a county was not over 100. 
lq ,„ ^significant increase in abundance of the corn borer In . 
Infl? v 938 °y mred ln the region of 35 counties surveyed in both years in 
14 ah number of borers per 100 plants more than doubled from 
•9 n 1933 to 34,1 m 1939. Significant increases took place in 22 of the in- 
