THE COLORADO POTATO-BEETLE. 
145 
about 1878. The insect has contrived by some means consi- 
derably to outstrip the prediction, and between 1871 and 1873, 
at any rate, it must have passed over nearly 300 miles of 
country. This astonishing rate of progress can hardly be due 
to the insect’s own exertions, and it seems probable that the 
rapidity with which it appears to be spreading in the densely 
populated eastern States must be owing to the increased traffic 
in these districts offering additional facilities of artificial 
transport. 
A striking point in the history of this unwelcome occupation 
of the cultivated low grounds of North America by a mountain 
beetle is that it has taken almost a direct easterly route across 
the continent, and that its advance has been at all times more 
rapid in the northern than in the southern districts. The 
American entomologists who have written most fully upon this 
beetle, Messrs. Walsh and Riley, remark especially upon this 
point ; and the former compares the advance of the insects 
through Illinois to that of General Sherman’s army in the late 
war, and says that “ the southern columns of the grand army 
lag far behind the northern columns.” 
According to Mr. Riley this peculiarity is to be accounted for 
by the supposition that the western potato-bug being essentially 
an Alpine species, thrives best and therefore spreads most 
rapidly in the cooler northern regions, and this view is borne 
out by the fact that even in the north a very hot summer 
destroys the insect. 
Of the actual extent of damage done to the potato crops in 
the districts which have been visited by these destructive in- 
sects we have no precise information, the only approach to an 
estimate being that of Mr. Walsh, who stated the probable loss 
by this cause in a small district at about 1,750,000 dollars. 
From the nature of the case, it is perhaps almost impossible to 
arrive at any exact computation. Nevertheless, the statistics 
published annually by the United States Department of Agri- 
culture -seem to indicate a falling off in the potato crops, which 
may be due to the ravages of the Doryphora. Thus, the total 
production of potatoes in all parts of the United States was as 
follows : — 
Bushels. Acres. Average per Acre. 
In 
1868..*. 
106,090,000 
from 
1,131,552 
94 
Bushels. 
In 
1869... 
133,886,000 
1,222,250 
109i 
i) 
In 
1870... 
114,775,000 
)) 
1,325,119 
86 
V 
In 
1872... 
— 113,516,000 
1,331,331 
85 
V 
The year 1869 seems to have been an exceptionally favour- 
able one for the growth of potatoes in all parts of the Union. 
Indeed, in Michigan, which had already been invaded by the 
Colorado beetle, the yield reached the enormous average of 155 
VOL. XIV. — NO. LV. L 
