July 7, 1923 
Platygaster vernalis , Hessian Fly Parasite 
4i 
same host, it was classified according to the condition of vernalis. Such 
cases were comparatively few. 
The number of hosts containing dead material recognized as vernalis 
was as a rule, exceedingly small. The cause of the death of vernalis in 
such cases could seldom be determined, although sometimes they ap¬ 
peared to have been eaten by predators. 1 
Fig. 5. Mortality of Platygaster vernalis as observed in collections of Hessian fly forms made at Mount 
Holly Springs, Pa., in 1919. (Table III.) 
In 1918 (Table III), by the 19th of July, the mortality of Platygaster 
vernalis reached 43.96 per cent and by August 27, the date of the last 
collection for that year, it had reached as high as 81.33 per cent. At 
that time the death of at least 45.51 per cent of the vernalis parasites was 
due to the competition of other Hessian fly parasites. It would be haz¬ 
ardous to say that any greater proportion were destroyed by this agency, 
Fig 6— Mortality of Platygaster vernalis, as observed in collections of Hessian fly forms made at Mount 
Holly Springs, Pa., in 1920. (Table III.) ' 
since the remaining 35.82 per cent could be accounted for by hosts con¬ 
taining dead unrecognizable matter and dead vernalis. 
In 1919 (Table III), by July 11, 60.03 P er cent of the vernalis had been 
destroyed. By October 10 of the same year 93.91 per cent had died. 
Of these at least 46.14 per cent were killed in competition with other 
hymenopterous parasites of the Hessian fly. 
