FLUCTUATION IN THE DISTRIBUTION OF THE COLORADO 
POTATO BEETLE 1 
By C. H. Batchelder 
Research Assistant , Department of Entomology , Cornell University 
INTRODUCTION 
Fluctuation in the abundance and distribution of the Colorado 
potato beetle (Leptinotarsa decemlineata) is a constantly observable 
phenomenon in a potato-growing region. So inconspicuous does this 
insect become during occasional years that some growers do not feel 
justified in using a poison with their early sprays. Furthermore, in 
any year the distribution of the species in a given locality is extremely 
uneven. Great variation is found in the percentage of infestation 
from field to field, from farm to farm, and from one locality to another, 
in the same year as well as over a period of years. No satisfactory 
explanation of the phenomena has been offered except that of para¬ 
sitism. Field studies, however, reveal certain variable factors operat¬ 
ing in a northern latitude to effect variation in the abundance of the 
Colorado potato beetle in adjacent fields and also an important factor 
which influences the abundance of the insect over a series of years. 
It may be desirable to set down evidence of the nature of these 
variables as well as certain conclusions that may be considered with 
profit by growers. 
FIELD1STUDIES 
The operation of these variables was demonstrated in field studies 
undertaken to determine whether correlation existed between the 
percentage of infestation and various environmental factors. The 
data in this study, involving six varieties, were taken during the period 
August 17 to 23, 1919, a year of comparatively fight infestation, 
in 12 townships of northern Maine, from 57 potato fields with a total 
of 786 acres. In contrast, data are used that were taken from the 
same fields, with a few exceptions, in a year of comparatively heavy 
infestation, during the interval August 23 to 25, 1921, from 27 fields 
totaling 273 acres. During the interval September 8 to 11, 1924, 
similar studies were undertaken in 3 counties in western New York 
in 28 fields totaling 226 acres. The conclusions derived from these 
studies have been confirmed by field observations in other northern 
potato-producing regions. The data taken at all fields being the 
same, included the following: Variety, acreage, date of planting, type 
of,soil, fertilizer, windage, slope, sprays, disease, condition of the crop, 
and the percentage of the plants infested. The percentage of in¬ 
festation figure was determined from field readings of 100 plants taken 
at random throughout the field, and was based on the presence or 
1 Received for publication Nov. 25, 1924; issued October, 1925. 
Journal of Agricultural Research, Vol. XXXI, No. 6 
Washington, D. C. Sept. 15,1925 
Key No. N. Y. 
(Comell)-6 
66850—25T-4 
(541) 
