Vol. 19 
Supplement to Nuralier 8 
Octotier 20,1939 
ESTIMTES OE DAMAGE BY THE EUROPEAN CORE BORER IN 1938 
AND A COMPARISON WITH 1937 ESTIMTES 
By A. M. Vance, Entomologist j 
Bureau of Entoraologj/’ and Plant ^arantine , 
United States Department of Agriculture ; 
A significant item in the consideration of the economic importance of an in- 
jurious insect, aside from information on the potential menace of the pest to 
crop production and the effect of its presence on agricultural practices, is an 
estimate of the money damage Being caused hy the insect over the area of its 
distribution, Eor the purpose of presenting a conservative picture of the 
economic importance of the European com Borer as a corn pest in 193^, gross 
estimates were prepared of the damage caused By the insect, Both to corn har- 
vested for grain and to swoet corn, within that portion of the infested terri- 
tory surveyed in the fall of 193^ to determine its relative aBundance, Although 
these estimates are necessarily approximate, it is Believed that they are Based 
on sound calculations and are sufficiently accurate for practical use. Compari- 
son has Been made Between estimates of d.amogc for 1937 '^d 193S, Basing the data 
for Both years on the more restricted area surveyed in 193S, No direct compari- 
son should Be attempted Between the 1937 ^^d 193^ estimates of corn Borer damage 
considered in this report end any yearly ostirAates presented previously in other 
reports. Because the areas involved are not compa.raBle, ■ 
i 
To obtain percentages of loss for corn Borer infestations of different in— | 
tensities, established daiaage indices of 3-P©rcent loss per Borer per plant in | 
corn haivested for gra.in, and of 8— percent losf? per Borer per plant in sweet 
com, were applied to the average number of Borers per 100 plants per county or; 
county group as determined from the fall— infestation survey* The same average 
Borer population figures were utilized for Both types of com in all cases e^ 
cept that for sweet corn in New Jersey in 193S, An extreme exaggeration of loss 
By the corn Borer in 193 S would have resulted from the utilization of the high 
population figures for the fall or second generation of the insect that year in 
lew Jersey in calculating the damage to the rather extensive acreage of sweet , 
corn in surveyed parts of the State, the greater part of which was affected 
principally By the much lighter first generation of the Borer. Consequently the 
percentage of loss calculated for the lower Borer populations found in New Jerse; 
lu 937 was applied to the 193 S values of the sw'eet com crop in the surveyed 
counties of the St-te. Eignir-^s on grain-corn production in Bushels were derived 
rom t e 1935 Agricalturad Census, and estimates of sweet com production were 
obtained By multiplying the coimty acreages of this crop given in the census By 
an average yield of 800 dozen ears per aero. All acreage figures were taken froi 
tue census. Crop values were obtained By applying current prices to tiie corn- 
production data, and the estimated Borer damage in dollars as computed from the 
igures on crop value and the calculrded percentage of loss By the insect, 
-535- UBRARY 
STATE PLANT BOARD 
