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Status of the Parasites as Determined by the 1939 Surveys 
Lydella str.hulans va,r, gri so scons H a D . — This ta„chinid was the most abundant of 
the three species of exotic parasites recorded in the Lake States area in 1939* 
However, contrary to results of previous years no increase was shown at my 
point. At Erie Township, Monroe County, Mich., and at Perkins Township, Erie 
County, Ohio, the percentage of parasitization remained approximately equal to 
that of 1939 » on about l 6 and J8 percent, respectively, at the two points. It 
appears that equilibrium with the host was attained by this parasite in 1932 
following releases at Perkins Township, Erie County, Ohio, in 1928 and at Erie 
Township, Monroe County, Mich., in 1932* The survey in Oregon mid Jerusalem 
Townships in Lucas County, Ohio, conducted to obtain data on the extent to whic" 
the parasite dispersed inland from marshland showed that as the distance from 
the shore increased the percentage of parasitization decreased rapidly. The 
average parasitization in strips 1 mile wide from the lake Erie shore line inla: 
is given in the following tabulation. 
Strip 
1 
2 
3 
4 
Par as i t i z at i 0 n 
Percent 
30oS 
13.3 
0„8 
0.1 
The highest percentage of parasitization in any collection was 63 • 9 
Collections along the Lake Erie shore from the Huron River to Cleveland and 
near the Lake St. Clair shore from Detroit to St, Clair River showed that L. 
grisescens was not present in those areas in sufficient numbers to be recovered 
by the means utilized. 
In the Eastern States area L. grisescens was recovered at all points sur- 
veyed, Prom the collections made in Middlesex County, Mass., it was recovered 
in somewhat larger numbers than in 1932 but wa,s still comparatively scarce there 
It continued its increase in the southeastern Massachusetts district and para- 
sitization of the borers observed at the close of 1939 avorn.ged 4.6 percent. 
It also continued to disperse, adding approximately 325 square miles to its 
known habitat. 
This dipterous parasite was recovered from 9 towns in the vicinity of Hart- 
ford., Conn. Its distribution at this point is shown on nap 1, where it may be 
noted, that borer parasitization was highest northwest and west of the point of 
liberation which was at the center of the area represented on the nap. This was 
also the case in 1938. That this westward dispersion is probably significant 
nay be readily shown by an inspection of the parasitization figures. Only J 
collections ( 19 percent of the 37 collections) made east of the release point 
produced L. grisescens . In all of these the rate of parasitization by this fly 
was very low and all but 1 of the J were located within 2 l/2 miles of the re- 
lease point. Of the 34 collections made west of the release point, 26 (j6 per- 
cent) gave L, grisescens and the prasitlze.tion was comparatively high, especial!' 
