54 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
Control 
During the last two years, Mr. Downes, in charge of our Victoria, 
B. C., laboratory, has had excellent success in destroying the egg masses 
by spraying with the miscible oil known as Dormoil. Various infested 
bushes and trees were sprayed in the first half of April with this oil in 
the strength of 1-12 and 1-15. For the larvae he has recommended, in 
general, a spray of Black Leaf 40 one ounce, whale oil soap 8 ounces, 
lead arsenate (powder) 2 ounces, water 3 gallons, repeating as often as 
necessary, and to be applied particularly for the young larvae. 
President A. G. Ruggles: We will now listen to a paper by R. L. 
Webster. 
FACTORS AFFECTING DAMAGE TO CROPS BY INSECTS 
By R. L. Webster, Fargo , No. Dakota 
Abstract 
The real significance of much insect damage is not fully appreciated, since it is 
often concealed. Much injury by insects is laid to other factors. The severity of 
damage by insects may be influenced greatly by temperature and moisture. Crops, 
the growth of which is retarded primarily because of lack of moisture will suffer 
more injury when attacked by insects than other crops not so retarded. Other 
conditions being equal, insect damage is more severe on the crop handicapped by 
reason of deficient moisture. Various types of soils in turn affect the severity of 
insect damage because of differences in their water holding capacity. 
Damage to crops by insects often is considered to be due mainly to a 
single factor; the abundance or scarcity of the particular insect or in¬ 
sects concerned. That other factors may be involved is not questioned, 
but the extent to which these other factors may be concerned is a matter 
that has received comparatively little attention. In the Great Plains 
area, that region between the Rocky mountains and the Mississippi 
valley, characterized as it is by a limited rainfall, certain of these other 
factors affecting crop losses by insects are brought quite forcibly to our 
attention. 
Factors Involved in Crop Losses 
In the Yearbook of the United States Department of Agriculture for 
1922, an attempt has been made to summarize the extent and causes of 
crop losses of various kinds so far as the wheat crop is concerned. 
Over a period of 14 years these estimates indicate average losses amount¬ 
ing to a total of 30%. The main factors listed are as follows; Deficient 
