204 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
percentage and intensity of infestation are used as an indication of. 
the success or failure of the advised seeding dates and of the magnitude 
of the menace that existed to fall sown wheat. 
Though only a matter of opinion, the advised seeding dates are 
considered good when the maximum infestation in any sample taken 
from sowings on or after these dates is less than ten percent of the 
infestation of any sample taken from sowings made before these advised 
dates. Intensity is the term used to represent the average number 
of fly forms per infested culm or plant. 
Flaxseeds from the late spring examination are disposed of in the same 
manner as those obtained in the fall except that fifty, to one hundred 
are dissected to determine the percentage of parasitism. 
The principal results of the late spring examination are the deter¬ 
mination for each experiment of the percentage and intensity of in¬ 
festation of the samples taken from all the sowings and the percentage 
of parasitism, determination and distribution of parasites of the flax¬ 
seeds thus obtained. This information is then used to indicate the 
probable status of the Hessian fly menace to fall sown wheat and thus 
is the basis for an opinion as to how much emphasis should be given 
to secure the observance of advised dates of seeding and other control 
measures the following fall. In addition to the information previously 
discussed the figures obtained serve as an indication of variations in 
the abundance of Hessian fly in different localities for the same year 
and in the same locality from year to year. 
Damage 
Considerable thought has been given to the possibility of devising 
some scheme of correlation of fall and spring infestation of Hessian fly 
with the amount of resultant damage as indicated by final yield. It 
seems quite obvious that damage and sometimes severe loss can be 
directly associated with either fall or spring infestation. In the case 
of abandonment of entire fields which sometimes occurs due to extreme¬ 
ly heavy and timely infestation, no index of injury is needed to predict 
the extent of reduction in yield at harvest time. Some damage must 
be caused by less severe but varying degrees of infestation but because 
of inconstant variation of other contributing factors, no satisfactory 
scheme has yet been developed by which the effect on final yield may 
be predicted with even a fair degree of dependability by a known 
percentage of infestation in fall or spring. 
