80 THE CHINCH BUG. 
S. A. Forbes has secured information of tbe occurrence of these insects 
in sufficient numbers to attract attention as early as 1823 in southern 
Illinois, and within 25 miles of New Harmony, Ind., where Thomas 
Say resided and did the most of his entomological work. 
REASONS FOR THE PRESENT THEORY OF DIFFUSION. 
It seems to me that in all of this we have good grounds for suppos- 
ing that the chinch bug occupied the most of the country prior to its 
occupancy by the white man, and that its first depredations were 
caused by its own advance coming in contact with the advance of 
civilization ; and the simultaneous cessation of forest and prairie fires, 
with the displacement of the native grasses by large areas of wheat, 
so combined that the points of contact were in Illinois, in the West, 
and Virginia and North Carolina in the East. Not until within the 
last fifteen years has the chinch bug been known to work serious and 
widespread injury east of the Allegheny Mountains, north of Virginia; 
and west of these mountains they have done scarcely any damage 
north and east of a line drawn from Chicago southeast to Cincinnati. 
Thousands of farmers in Ohio never saw a chinch bug until within the 
last four years, and there are thousands more in northwestern Ohio, 
southern Michigan, and northern Indiana that, even yet, would not be 
able to recognize one were they to see it among their growing grain, or 
even if in abundance. But in considering this matter the fact must be 
borne in mind that timothy meadows are not burned over annually as 
were the forests and prairies, and the stubble does not die with the 
harvesting of the crop as in wheat, and therefore does not necessitate 
annual migrations in order to preserve life. In a timothy meadow the 
species may live on and reproduce year after year without ever being 
obliged to abandon the field. It was the wheat fields of the West that 
the east-bound, macropterous tide of migration found confronting it in 
Illinois, and the smaller fields of grain and timothy meadows that the 
combined macropterous and brachypterous forms, more or less maritime 
and north bound, came in contact with along the Atlantic coast, while 
at the present time the two tides of migration have met in north- 
eastern Ohio and northern Indiana. 
In fig. 17 I have illustrated the theoretical directions and courses 
taken by each of these tides of migrations from the tropical regions, 
and in fig. 1 the areas over which the species is now known to occur 
in Central and North America are indicated. 
I believe that this same course of migration has been pursued, at least 
in the West, by the several species of Diabrotica, and especially D. 
longicornis Say, and to a less extent by another species of Hemiptera, 
Murgantia histrionica Hahn., and possibly also by Dynastes tityiis Linn., 
while the two latter with others are now working northward along the 
Atlantic coast. Besides, the westward tide of migration has been fol- 
lowed in all probability by Pieris rapce Linn., Phytonomus punctatus 
