38 
Journal of Agricultural Research 
Vol. XXV, No. I 
of space. Occasionally adults have been found to emerge and oviposit 
during the autumn, but this is exceptional, and field observations indicate 
that eggs deposited at that season fail to mature. 
Fig. 2.—Periods of occurrence of the various stages of Platygaster vernalis as found from examinations made 
during the years from 1918 to 1921, inclusive. The dates on which the examinations were made are 
indicated at the bottom of the diagram. 
Figure 3 shows the rate of development of the various stages of Platy¬ 
gaster vernalis from May 17 to October 18. These data were obtained 
'by the dissection of Hessian fly stages collected in lots of 100 or more 
Fig. 3.—Rate of development of the various stages of Platygaster vernalis as they occurred during the 
year 1919 on farm at Mount Holly Springs, Pa. The dates on which examinations were made are indi* 
cated at the bottom of the diagram. 
at certain dates during 1919, as indicated at the base of the diagram. 
All of the collections were made at Mount Holly Springs, Pa. The rather 
late occurrence of vernalis adults during that year was probably due 
entirely to meteorological conditions. 
