. 132 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
will in many cases mean quite a change in cultural practices but this 
seems unavoidable. 
In conclusion let me say that this paper has been written largely with 
the object of arousing discussion, so that all interested may thereby 
receive helpful suggestions. 
PLOUGHING AS A FACTOR IN CONTROL OF THE EUROPEAN 
CORN BORER (PYRAUSTA NUBILALIS HUBNER) IN ONTARIO 
CANADA 
By H. G. Crawford, Entomological Branch, Dominion Department of Agriculture , 
Ottawa 
Abstract 
Clean ploughing either in the fall or spring is the important control measure in the 
Canadian infestation in the disposal of that portion of the European Corn Borer 
population left in the field in the stubble and refuse after the removal of the crop. 
The larvae in the material ploughed down practically all come to the surface sooner 
or later with a very slight mortality. When the ploughing is done in the very early 
fall most of the larvae come to the surface before winter. With later ploughings an 
increasing proportion fail to come to the surface and remain below ground till spring. 
Following spring ploughings the larvae come to the surface in a similar manner and 
at a rate depending somewhat upon the date of ploughing. In all cases the upward 
movement is practically complete by June 5th. After the larvae come to the surface, 
which they do at night, they wander about somewhat; a small proportion enter the 
crop refuse if any is upon the surface and eventually come to maturity as moths, the 
balance, or in the absence of suitable shelter all the larvae, settle under clods of earth 
or in the soil and fail to produce sufficient moths to be of real importance. The 
larvae in the open soil simply disappear and little is known quantitatively about the 
various factors which cause this reduction. In a field where the refuse contained 
33,800 larvae per acre, clean ploughing in spring or fall resulted in the virtual an¬ 
nihilation of the larval population by the time that pupation would normally be ex¬ 
pected the following year. 
Under Ontario conditions and particularly in the corn-seed growing 
counties of Essex and Kent, the most difficult problem in the control 
of the European Corn Borer is to dispose of the larvae left in the crop 
refuse naturally present in the field after harvest. This phase of the 
problem assumes particular prominence on account of the fact that the 
insect in Ontario is essentially single brooded and the over-wintering 
larval reserve in crops and plants other than corn is negligible as yet. 
As this condition is likely to obtain elsewhere a report on some of the 
results of the Canadian investigation may be of interest to other ento¬ 
mologists. 
Some of the tentative conclusions and results of the Canadian in- 
