4 
CIRCULAR 816, U. S. DEPARTMENT OF AGRICULTURE 
Table 1 .—Average egg-pod distribution per square foot by habitats for areas 
under study in the northern Great Plains, 1936-43 
Habitat 
1936 
1937 
1938 
1939 
1940 
1941 
1942 
1943 
Average 
1936-43 
Field margins.. . 
0.761 
0.741 
1.241 
0.725 
0.862 
0.773 
0.976 
0.816 
0.862 
Idle land. 
.581 
.394 
.654 
.624 
.519 
.615 
.553 
.440 
.547 
Pasture. 
.400 
.240 
.575 
1.000 
.301 
.300 
.095 
.385 
.412 
Legumes. 
.278 
.514 
.421 
.574 
.418 
.353 
.355 
.314 
.403 
Flax stubble. 
.101 
.718 
.267 
.317 
.351 
Small-grain 
stubble. 
.336 
.546 
.356 
.587 
.249 
.259 
.279 
.162 
.347 
Prairie. 
.526 
.387 
.369 
.305 
.389 
.293 
.120 
.169 
.320 
Crested 
wheatgrass. . . 
.375 
.600 
.580 
.280 
.140 
.175 
.182 
.196 
.316 
Wild-hay 
meadows. 
.000 
.250 
.730 
.090 
.214 
.280 
.040 
.000 
.200 
River-bottom 
land. 
.050 
.000 
.330 
.000 
.330 
.120 
.200 
.120 
.144 
Truck crops.... 
.390 
.207 
.133 
.210 
.006 
.107 
.000 
.013 
.133 
Corn. 
.165 
.174 
.180 
.104 
.134 
.190 
.032 
.023 
.125 
Sorghums. 
.185 
.249 
.027 
.000 
.115 
The data in table 1 are quantitative only to the extent that they indi¬ 
cate the egg-pod density in the respective habitats. To apply these data 
to general field conditions, the percentage of the total area occupied by 
each habitat must be considered. For example, although of all the habi¬ 
tats field margins contain the heaviest populations, they comprise only 
about 5 percent of the total area. Conversely, small-grain fields, which 
have moderate populations, comprise about 80 percent of the farmed area. 
In the 10-county special survey, grainfields predominated and crop dif¬ 
ferences were not prominent; hence, crop-type differences were not con¬ 
sidered in further analysis of these data, except for distinction between 
field and margin. 
In Fields and Margins 
One of the first essentials in the development of a dependable survey 
method is a knowledge of egg-pod distribution within fields. One opinion 
was that more eggs were laid near the edge of the field than near the 
center. To obtain more definite data, egg sampling was conducted in 10 
counties in north-central Montana, samples being taken from 70 fields 
located at random in each county. The number of fields of each major 
crop sampled was in proportion to the acreage of that crop in the county. 
In each field 5 pairs of -square foot units of soil were taken at equal 
distances apart in a straight line from the edge of the field to the center. 
Ten F 2 _s quare-foot units were also taken in the uncultivated margin 
of each field, 5 units in the half nearest the crop, and the other 5 in the 
half nearest the road. 
The mean egg-pod population for each field and margin location is 
shown by counties in table 2. It will be noted that populations for the 
different locations within fields tended to vary at random. In the margins 
numbers tended to be greater in the half near the field than in the half 
near the road. 
