Statue of Parasites as Determined, "by the 1937 Surveys 
Lydella stabulans grisescens R. D. ; — This tachinid parasite was of 
primary importance in the Lake States area at all points adjacent to 
Lake Erie. In Jerusalem Township, Lucas County, Ohio, where the parasite 
has been present for 8 years, the 1937 survey showed that the area from 
which it was recoverable had extended considerably to the south and east. 
Samples from five of the fields examined at this point showed parasitization 
percentages of 69 . 2 , 6 l.O, 50*5* *+ 8 . 4 , and 4 l. 7 » respectively. 
Table 3 - — Annual fall parasitization by Lydella grisescens about the 
Jerusalem Township, Lucas County, Ohio/ release point* " 
Year 
Parasitization 
within radius of release 
3-#' miles 
• 7 ^ miles 
Percent 
: Percent 
1932 
0.3 
: — 
1933 
2.8 
• — 
1934 
6.3 
: — . 
1935 — 
7.6 
: • 4.4 
1936 
10.0 
: 7.0 
1937 
22 .. 5 
: 9.6 
The progressive increase in parasitization, as shown by table 3 » indi- 
cates that Lydella grisescens did not reach equilibrium previous to 1937 » 
even within the 3 ? mile radius of the release point. The parasitization 
within the continuously parasitized area at the Jerusalem colony site 
amounted to 20 percent. This is the highest parasitization recorded at any 
point in either area and indicates an environment particularly favorable 
to the development of the species. 
In Erie Township, Monroe County, Mich., and in Perkins Township, Erie 
County, Ohio, two of the oldest colony sites in the Lake States area, the 
parasitization by Lydella grisescens showed a remarkable increase in 1937 
over that of 1936, the percentage of increase at the two points being 68.6 
and 918 . 3 > respectively. Observations designed to determine the distri- 
bution of this tachinid in the Maumee River Valley and northward into 
Michigan along the western shore of Lake Erie over an area 20 miles long 
and 9 miles wide, showed L. grisescens to be present and in greater abun- 
dance in all the quadrates in the vicinity of marshland bordering the 
lake or streams within the area observed. With one exception Lydella 
was not found at a greater distance than . 4' miles from the lake shore 
see map 1) . 
This imported tachinid was recovered from all five of the regions 
in which host collections were made in the East. It occurred in maximum 
abundance in a restricted area extending northeasterly in the vicinity of 
Taunton, Mass. Parasitizations of about 15 percent occurred in samples 
taken between Taunton and Fall River, Mass. L. grisescens was known to be 
present at the close of 1937 in a territory totaling over 837 square 
miles m the Eastern States area. . ^ 
