Populations of the army cutworm, Chorizagrotis auxiliaris (Grote), tended to be higher in winter barley than winter wheat planted side by side in the same field. Highest populations occurred in barley within 30 feet of the adjoining wheat. Distribution of larvae in linear 1-foot samples agreed closely with the Poisson. Practical application of these results are discussed

Pruess, K. P.

English

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University of Nebraska - Lincoln
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Faculty Publications: Department of Entomology Entomology, Department of
4-1961
Distribution of Army Cutworm Larvae in Wheat
and Barley Fields
K. P. Pruess
University of Nebraska, North Platte Experiment Station
Follow this and additional works at: http://digitalcommons.unl.edu/entomologyfacpub
Part of the Agriculture Commons, and the Entomology Commons
This Article is brought to you for free and open access by the Entomology, Department of at DigitalCommons@University of Nebraska - Lincoln. It has
been accepted for inclusion in Faculty Publications: Department of Entomology by an authorized administrator of DigitalCommons@University of
Nebraska - Lincoln.
Pruess, K. P., "Distribution of Army Cutworm Larvae in Wheat and Barley Fields" (1961). Faculty Publications: Department of
Entomology. 674.
http://digitalcommons.unl.edu/entomologyfacpub/674
 
 
 
Published in Journal of Economic Entomology 54:2 (April 1961), pp. 250–252; doi: 10.1093/jee/54.2.250. 
Copyright © 1961 Entomological Society of America; published by Oxford University Press. Used by 
permission. 
Accepted September 12, 1960; published April 1, 1961. 
 
 
Distribution of Army Cutworm Larvae 
in Wheat and Barley Fields1 
 
 
K. P. Pruess 
 
University of Nebraska, North Platte Experiment Station, North Platte, Nebraska, USA 
 
Abstract 
Populations of the army cutworm, Chorizagrotis auxiliaris (Grote), tended to be higher in winter bar-
ley than winter wheat planted side by side in the same field. Highest populations occurred in barley 
within 30 feet of the adjoining wheat. Distribution of larvae in linear 1-foot samples agreed closely 
with the Poisson. Practical application of these results are discussed. 
 
The army cutworm, Chorizagrotis auxiliaris (Grote), is an important pest of wheat, barley, 
alfalfa, and other crops in Nebraska. Winter barley, because of wheat acreage allotments, 
is becoming of increasing importance in western Nebraska and has been especially suscep-
tible to cutworm injury. Whether this susceptibility to injury might be caused by higher 
cutworm populations, as reported by farmers, seemed worthy of investigation. 
 
Methods 
 
Six comparisons of larval populations were made in 1959 using paired winter wheat and 
barley fields on the same farms in Keith County. Fields were selected which had received 
similar cultural practices and were seeded about the same time. In no case was there any 
barrier between the paired fields with a maximum of 2 feet of cultivated ground separating 
the two. Sampling was begun 100 feet into each field from the adjoining road and contin-
ued at 10-foot intervals for another 90 feet parallel to the common boundaries. Paired sam-
ples were taken at distances of 3, 10, 20, 30, 50, and 100 feet into each crop perpendicular 
to the common boundary. One linear foot of soil was examined on each side of the row 
nearest these measured distances. The width of these sample units varied from 8 to 12 
inches, depending on row spacing, but always included the entire distance to the next row. 
PR U E S S ,  J O U R N A L  O F  E C O N O M I C  E N T O M O L O G Y  5 4  (1 9 6 1 )  
2 
Row spacing was the same in each pair of fields sampled, and all rows ran parallel to the 
common border. This sampling procedure, while not allowing actual comparisons of pop-
ulations between different pairs of fields without adjusting for sample width, clearly de-
fined differences between wheat and barley in each pair of fields. Linear-foot counts were 
transformed by √x + 1 prior to analysis and Duncan’s (1955) Multiple Range Test was used 
to make comparisons. 
 
Results 
 
Comparisons of populations at different distances into paired wheat and barley fields from 
the common boundary are given in Table 1. These results are presented graphically in Fig-
ure 1 in terms of actual populations rather than transformed values. 
 
Table 1. Mean number of army cutworm larvae per linear foot of row at different distances from 
the common boundary in six paired wheat and barley fieldsa 
 Fieldb 
Feet into Field 1 2 3 4 5 6 
Wheat       
100 1.27 cdef 1.28 abc 1.14 de 1.46 e 1.39 cd 1.52 abc 
50 1.21 def 1.18 bed 1.18 cd 1.59 bcde 1.40 cd 1.55 abc 
30 1.16 efg 1.12 cd 1.18 cd 1.52 de 1.63 abc 1.69 ab 
20 1.09 fg 1.l2 cd 1.12 de 1.62 bcde 1.61 bc 1.79 a 
10 1.04 g 1.20 bcd 1.02 f 1.55 cde 1.71 ab 1.38 cd 
3 1.04 g 1.08 d 1.06 ef 1.75 abcd 1.31 d 1.48 bcd 
Barley       
3 1.35 bcd 1.39 a 1.53 1.67 bcde 1.55 bcd 1.60 abc 
10 1.40 abc 1.35 ab 1.32 ab 1.76 abcd 1.64 abc 1.65 abc 
20 1.52 a 1.38 a 1.36 a 1.84 ab 1.78 ab 1.46 bcd 
30 1.29 bcde 1.27 abc 1.28 ab 1.96 a 1.89 a 1.54 abc 
50 1.32 bcde 1.31 ab 1.26 bc 1.82 abc 1.62 bc 1.49 bcd 
100 1.44 ab 1.29 abc 1.32 ab 1.79 abcd 1.54 bcd 1. 22 d 
a. Data transformed by √x + 1. 
b. Any two means in the same column not followed by the same letter are significantly different at the 5% 
level. 
 
  
PR U E S S ,  J O U R N A L  O F  E C O N O M I C  E N T O M O L O G Y  5 4  (1 9 6 1 )  
3 
 
 
Figure 1. Army cutworm populations in six paired wheat-barley fields at different 
distances from the common boundaries. 
 
Significantly higher populations were found in barley than in wheat in five of the six 
paired fields. In Field 6 wheat had slightly but not significantly more cutworms than bar-
ley. Greatest fluctuations in cutworm populations occurred within 30 feet of the common 
boundary. In no case was there a significant difference between samples taken at 50 and 
100 feet into either crop from this common border, and counts made at these distances 
likely were more representative of the field as a whole. Using only samples taken at 50 and 
100 feet as a basis for comparing the two crops, barley was still found to have significantly 
higher populations in four fields with no difference in two. 
Samples taken across wheat and barley parallel to the common boundary showed sig-
nificant differences to exist in that direction only in Field 3. In this field there were more 
cutworms in both wheat and barley in the first 50 feet nearer the road. Heavier marginal 
infestations have been observed to occur commonly in both crops. Sampling areas in this 
study were purposely located 100 feet away from adjoining roads to avoid such variation, 
leaving only the effect of the wheat-barley boundary to explain. 
PR U E S S ,  J O U R N A L  O F  E C O N O M I C  E N T O M O L O G Y  5 4  (1 9 6 1 )  
4 
Although varying in distance and intensity, the most notable feature revealed by these 
samples was a peak population in barley within 30 feet of the common boundary. This 
effect was noted in five of the six fields. Also in all but Field 4 this peak was accompanied 
by lower counts in wheat within 20 feet of the boundary. These peaks and depressions 
always fell within about 30 feet of each other. It would appear that winter barley, under 
identical cultural practices, had higher cutworm populations than wheat and that the fac-
tor responsible was operating most strongly along the boundary between the two crops. 
This effect was most marked in fields that had lower populations. Although the reasons 
for this larval distribution are unknown, certain practical uses may be made of this infor-
mation without knowledge of its causes. 
 
Practical Application of Results 
 
When making surveys for the army cutworm, it would appear highly desirable that sam-
ples be taken 50 to 100 feet or more away from any road or adjoining field. As shown, 
samples taken within 30 feet of the field edge may give highly misleading estimates of the 
population occurring over the field as a whole. Stratified random samples, when econom-
ically feasible, would be even more appropriate. Such a sampling procedure should cer-
tainly be used when determining the need for control measures. It seems likely that in 
many cases only the more heavily infested border of a field would warrant treatment. 
In research work, the design of the experiment should take into consideration these 
marginal changes in population. If uniform infestations are desired, location of plots as 
near the center of a field as possible would be indicated. If field margins are to be used for 
convenience or to obtain higher infestations, it would seem advisable to place blocks of 
plots parallel to these margins. Field corners, in which variation would be expected to oc-
cur in two directions, should be avoided, if possible, or a design such as a latin square used 
that will permit easy removal of both row and column effects. 
 
Mathematical Distribution of Larvae 
 
Larval counts in linear 1-foot samples in all fields studied agreed closely with the Poisson 
distribution. Table 2 gives the observed and theoretical distributions for one pair of fields. 
Counts in other fields fitted the Poisson equally well. 
  
PR U E S S ,  J O U R N A L  O F  E C O N O M I C  E N T O M O L O G Y  5 4  (1 9 6 1 )  
5 
Table 2. Frequency distribution of army cutworm larvae in linear 1-foot samples and comparison 
with Poisson distribution 
 Field II—Wheat  Field II—Barley 
Larvae 
per foot 
Observed 
Frequency 
Expected 
Frequency 
 Observed 
Frequency 
Expected 
Frequency 
0 28 29.1  17 16.7 
1 40 41.2  37 32.9 
2 33 29.2  29 32.5 
3 14 13.8  20 21.4 
4 3 4.9  8 10.6 
5 2 1.4  5 4.2 
6+ 0 0.4  4 1.7 
Total 120 120.0  120 120.0 
 χ2 = 0.99 
P = > 0.90 
 χ 2 = 3.26 
P = > 0.65 
 
A square root transformation suggested by Snedecor (1956) for low counts agreeing 
with the Poisson was used in this study to gain precision. However, when several samples 
are pooled and totals analyzed, as is commonly done in chemical control studies, the use 
of a transformation will not ordinarily lead to conclusions any different from those reached 
by an analysis of the original data. 
 
Note 
1. Published with approval or the Director as Paper No. 1064 Journal Series, Nebraska Agricultural 
Experiment Station. This study was supported by a research grant from the Nebraska Wheat 
Commission. Accepted for publication September l2, 1960. 
 
References Cited 
 
Duncan, D. B. 1955. .Multiple range and multiple F tests. Biometrics 11: 1–42. 
Snedecor, G. W. 1956. Statistical Methods. Iowa State College Press, Ames, Iowa. 5th ed. 534 pp. 


Distribution of Army Cutworm Larvae in Wheat and Barley Fields

DigitalCommons@University of Nebraska

University of Nebraska - LincolnDigitalCommons@University of Nebraska - LincolnFaculty Publications: Department of Entomology Entomology, Department of4-1961Distribution of Army Cutworm Larvae in Wheatand Barley FieldsK. P. PruessUniversity of Nebraska, North Platte Experiment StationFollow this and additional works at: http://digitalcommons.unl.edu/entomologyfacpubPart of the Agriculture Commons, and the Entomology CommonsThis Article is brought to you for free and open access by the Entomology, Department of at DigitalCommons@University of Nebraska - Lincoln. It hasbeen accepted for inclusion in Faculty Publications: Department of Entomology by an authorized administrator of DigitalCommons@University ofNebraska - Lincoln.Pruess, K. P., "Distribution of Army Cutworm Larvae in Wheat and Barley Fields" (1961). Faculty Publications: Department ofEntomology. 674.http://digitalcommons.unl.edu/entomologyfacpub/674   Published in Journal of Economic Entomology 54:2 (April 1961), pp. 250–252; doi: 10.1093/jee/54.2.250. Copyright © 1961 Entomological Society of America; published by Oxford University Press. Used by permission. Accepted September 12, 1960; published April 1, 1961.   Distribution of Army Cutworm Larvae in Wheat and Barley Fields1   K. P. Pruess  University of Nebraska, North Platte Experiment Station, North Platte, Nebraska, USA  Abstract Populations of the army cutworm, Chorizagrotis auxiliaris (Grote), tended to be higher in winter bar-ley than winter wheat planted side by side in the same field. Highest populations occurred in barley within 30 feet of the adjoining wheat. Distribution of larvae in linear 1-foot samples agreed closely with the Poisson. Practical application of these results are discussed.  The army cutworm, Chorizagrotis auxiliaris (Grote), is an important pest of wheat, barley, alfalfa, and other crops in Nebraska. Winter barley, because of wheat acreage allotments, is becoming of increasing importance in western Nebraska and has been especially suscep-tible to cutworm injury. Whether this susceptibility to injury might be caused by higher cutworm populations, as reported by farmers, seemed worthy of investigation.  Methods  Six comparisons of larval populations were made in 1959 using paired winter wheat and barley fields on the same farms in Keith County. Fields were selected which had received similar cultural practices and were seeded about the same time. In no case was there any barrier between the paired fields with a maximum of 2 feet of cultivated ground separating the two. Sampling was begun 100 feet into each field from the adjoining road and contin-ued at 10-foot intervals for another 90 feet parallel to the common boundaries. Paired sam-ples were taken at distances of 3, 10, 20, 30, 50, and 100 feet into each crop perpendicular to the common boundary. One linear foot of soil was examined on each side of the row nearest these measured distances. The width of these sample units varied from 8 to 12 inches, depending on row spacing, but always included the entire distance to the next row. PR U E S S ,  J O U R N A L  O F  E C O N O M I C  E N T O M O L O G Y  5 4  (1 9 6 1 )  2 Row spacing was the same in each pair of fields sampled, and all rows ran parallel to the common border. This sampling procedure, while not allowing actual comparisons of pop-ulations between different pairs of fields without adjusting for sample width, clearly de-fined differences between wheat and barley in each pair of fields. Linear-foot counts were transformed by √x + 1 prior to analysis and Duncan’s (1955) Multiple Range Test was used to make comparisons.  Results  Comparisons of populations at different distances into paired wheat and barley fields from the common boundary are given in Table 1. These results are presented graphically in Fig-ure 1 in terms of actual populations rather than transformed values.  Table 1. Mean number of army cutworm larvae per linear foot of row at different distances from the common boundary in six paired wheat and barley fieldsa  Fieldb Feet into Field 1 2 3 4 5 6 Wheat       100 1.27 cdef 1.28 abc 1.14 de 1.46 e 1.39 cd 1.52 abc 50 1.21 def 1.18 bed 1.18 cd 1.59 bcde 1.40 cd 1.55 abc 30 1.16 efg 1.12 cd 1.18 cd 1.52 de 1.63 abc 1.69 ab 20 1.09 fg 1.l2 cd 1.12 de 1.62 bcde 1.61 bc 1.79 a 10 1.04 g 1.20 bcd 1.02 f 1.55 cde 1.71 ab 1.38 cd 3 1.04 g 1.08 d 1.06 ef 1.75 abcd 1.31 d 1.48 bcd Barley       3 1.35 bcd 1.39 a 1.53 1.67 bcde 1.55 bcd 1.60 abc 10 1.40 abc 1.35 ab 1.32 ab 1.76 abcd 1.64 abc 1.65 abc 20 1.52 a 1.38 a 1.36 a 1.84 ab 1.78 ab 1.46 bcd 30 1.29 bcde 1.27 abc 1.28 ab 1.96 a 1.89 a 1.54 abc 50 1.32 bcde 1.31 ab 1.26 bc 1.82 abc 1.62 bc 1.49 bcd 100 1.44 ab 1.29 abc 1.32 ab 1.79 abcd 1.54 bcd 1. 22 d a. Data transformed by √x + 1. b. Any two means in the same column not followed by the same letter are significantly different at the 5% level.    PR U E S S ,  J O U R N A L  O F  E C O N O M I C  E N T O M O L O G Y  5 4  (1 9 6 1 )  3   Figure 1. Army cutworm populations in six paired wheat-barley fields at different distances from the common boundaries.  Significantly higher populations were found in barley than in wheat in five of the six paired fields. In Field 6 wheat had slightly but not significantly more cutworms than bar-ley. Greatest fluctuations in cutworm populations occurred within 30 feet of the common boundary. In no case was there a significant difference between samples taken at 50 and 100 feet into either crop from this common border, and counts made at these distances likely were more representative of the field as a whole. Using only samples taken at 50 and 100 feet as a basis for comparing the two crops, barley was still found to have significantly higher populations in four fields with no difference in two. Samples taken across wheat and barley parallel to the common boundary showed sig-nificant differences to exist in that direction only in Field 3. In this field there were more cutworms in both wheat and barley in the first 50 feet nearer the road. Heavier marginal infestations have been observed to occur commonly in both crops. Sampling areas in this study were purposely located 100 feet away from adjoining roads to avoid such variation, leaving only the effect of the wheat-barley boundary to explain. PR U E S S ,  J O U R N A L  O F  E C O N O M I C  E N T O M O L O G Y  5 4  (1 9 6 1 )  4 Although varying in distance and intensity, the most notable feature revealed by these samples was a peak population in barley within 30 feet of the common boundary. This effect was noted in five of the six fields. Also in all but Field 4 this peak was accompanied by lower counts in wheat within 20 feet of the boundary. These peaks and depressions always fell within about 30 feet of each other. It would appear that winter barley, under identical cultural practices, had higher cutworm populations than wheat and that the fac-tor responsible was operating most strongly along the boundary between the two crops. This effect was most marked in fields that had lower populations. Although the reasons for this larval distribution are unknown, certain practical uses may be made of this infor-mation without knowledge of its causes.  Practical Application of Results  When making surveys for the army cutworm, it would appear highly desirable that sam-ples be taken 50 to 100 feet or more away from any road or adjoining field. As shown, samples taken within 30 feet of the field edge may give highly misleading estimates of the population occurring over the field as a whole. Stratified random samples, when econom-ically feasible, would be even more appropriate. Such a sampling procedure should cer-tainly be used when determining the need for control measures. It seems likely that in many cases only the more heavily infested border of a field would warrant treatment. In research work, the design of the experiment should take into consideration these marginal changes in population. If uniform infestations are desired, location of plots as near the center of a field as possible would be indicated. If field margins are to be used for convenience or to obtain higher infestations, it would seem advisable to place blocks of plots parallel to these margins. Field corners, in which variation would be expected to oc-cur in two directions, should be avoided, if possible, or a design such as a latin square used that will permit easy removal of both row and column effects.  Mathematical Distribution of Larvae  Larval counts in linear 1-foot samples in all fields studied agreed closely with the Poisson distribution. Table 2 gives the observed and theoretical distributions for one pair of fields. Counts in other fields fitted the Poisson equally well.   PR U E S S ,  J O U R N A L  O F  E C O N O M I C  E N T O M O L O G Y  5 4  (1 9 6 1 )  5 Table 2. Frequency distribution of army cutworm larvae in linear 1-foot samples and comparison with Poisson distribution  Field II—Wheat  Field II—Barley Larvae per foot Observed Frequency Expected Frequency  Observed Frequency Expected Frequency 0 28 29.1  17 16.7 1 40 41.2  37 32.9 2 33 29.2  29 32.5 3 14 13.8  20 21.4 4 3 4.9  8 10.6 5 2 1.4  5 4.2 6+ 0 0.4  4 1.7 Total 120 120.0  120 120.0  χ2 = 0.99 P = > 0.90  χ 2 = 3.26 P = > 0.65  A square root transformation suggested by Snedecor (1956) for low counts agreeing with the Poisson was used in this study to gain precision. However, when several samples are pooled and totals analyzed, as is commonly done in chemical control studies, the use of a transformation will not ordinarily lead to conclusions any different from those reached by an analysis of the original data.  Note 1. Published with approval or the Director as Paper No. 1064 Journal Series, Nebraska Agricultural Experiment Station. This study was supported by a research grant from the Nebraska Wheat Commission. Accepted for publication September l2, 1960.  References Cited  Duncan, D. B. 1955. .Multiple range and multiple F tests. Biometrics 11: 1–42. Snedecor, G. W. 1956. Statistical Methods. Iowa State College Press, Ames, Iowa. 5th ed. 534 pp. 

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Distribution of Army Cutworm Larvae in Wheat and Barley Fields

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