The Colorado Potato-Beetle. 
373 
hvbernates a few inches below the surface of the soil. Although 
it is true that the zone of country now occupied by the beetle has 
the same mean annual temperature (50') as the South of England, 
yet the summer and winter temperatures are widely different, 
the mean temperature for July in these parts of America being 
7i'\ and for January 32^; whilst in the South of England, it is 
G3 and 40' respectively for the same months. The more 
uniform humidity of Xorth-VVestern Europe throughout the year 
is also an element to be taken into consideration. The effect of 
this wide climatic difference is strikingly shown by the different 
course of the generations of those native European species which 
are nearest allied to the potato-beetle, i.e. the ChrijsotnelcB. These 
asree with the American insect in hvbernatin<; in the adult or 
beetle state, and awakening in spring to feed on their respective 
plants, and propagate their kind ; but they differ in having only 
one generation during the season, instead of three, and in their 
much lower fecundity, the females laying from 30 to GO eggs 
onlv in each generation, whilst the potato-beetle lays from 1000 to 
1200. All doubts respecting this disputed point have been set 
at rest by Mr. Daniels, of Wisconsin, who recently obtained 1200 
ova from one individual. It is an incredible supposition that a 
species of insect adapted to climatic conditions so entirely 
different, and presenting physiological features so incompatible 
with the influences it would encounter in Europe, could ever 
become acclimatised here. An important fact in confirmation 
of this view is supplied by a Report recentlv published by Lieut. 
VV. L. Carpenter, of the United States Geological Survey, of his 
investigations in 1873, namely, that the beetle has not yet 
passed to the west of the Rocky Mountains. " Not a single 
specimen," he says, " has been seen west of the dividing ridge." 
It has, therefore, not yet faced the adverse climatic conditions 
of the Pacific coast, which nearlv resemble those of Western 
Europe. It is right, however, to add, that Lieut. Carpenter 
believes it probable the insect will ultimately make its appear- 
ance in that region. 
Thus, even if we give all due weight to the great adaptability 
to new conditions which the beetle has shown during its progress 
over half the American Continent, it seems an untenable assump- 
tion that it can carry this so far as to establish itself in Western 
Europe. If it should do so, it would be an unprecedented case, 
and falsify all previous experience. Certainly the creature has 
developed an extraordinary flexibility of constitution and habits 
since it left its quiet home in the Rocky Mountains, and we 
cannot be quite sure what it will eventually do. We hear, for 
instance, of its attacking thistles after clearing the potato-fields I 
It enters hot-houses and devours all the tender tomato and egg- 
plants. Most of the wild species of Solanum are pounced upon 
