42 
Journal of Agricultural Research 
Vol. XXV, No. r 
In 1920 (Table III), by July 21, 85.27 per cent were destroyed, and 
by the 27th of November the mortality had reached 96.08 per cent. 
Although other parasites undoubtedly were responsible for the death 
of many of these, the figures on this date show such a high percentage 
of puparia containing dead, unrecognizable matter and dead Platygaster 
vernalis that the entire 96.08 per cent could not be assumed as having been 
killed in competition with other parasites. 
In 1921 by the 12th of July (Table III), there was a mortality of ver¬ 
nalis to the extent of 78.97 per cent and by September 23 the percentage 
of death reached 92.11 per cent. While in the results of this last exami¬ 
nation the death of nearly all of the vernalis could be accounted for by 
the large number of puparia containing dead unrecognizable matter and 
dead P. vernalis , yet the figures from the collection taken June 21 of the 
same year show that fully 31.64 per cent had already been killed as early 
as June by other hymenopterous parasites. 
From the foregoing observations the following conclusions may be 
deduced• 
(1) During each year the death rate of Platygaster vernalis was very 
high, being not less than 81.33 per cent for any one year, and in 1920 
being as high as 96.08 per cent. 
(2) A large percentage of the mortality of P. vernalis was due to com¬ 
petition with other Hessian fly parasites. 
(3) During the years 1918, 1920, and 1921 for the localities under obser¬ 
vation, P. vernalis was more effective than all other parasites of the 
spring generation of the Hessian fly combined. 
It should be stated that although the attacks of the other parasites 
are highly detrimental to the multiplication of Platygaster vernalis , yet 
they supplement the latter sufficiently well to effect a very high death 
rate of the Hessian fly. They also act as a safeguard in case of scarcity 
of vernalis. In all cases, moreover, the hyperparasitism appears to be 
entirely accidental. It would therefore be unwise to discount too greatly 
the value of the other parasites. 
