64 
FIRST ANNUAL REPORT OF THE 
INSECTS INFESTING THE PLUM. — On the Fruit. 
CHAPTER XI. — The Plum Curculio. ( Conotrachelus nenuphar, Herbst.) 
In tlie Practical Entomologist (Yol. II. pp. 75-9) I have dilated so fully on the Nat¬ 
ural History of this pestilent little Snout-beetle, and on the most approved methods of 
fighting it, that it will only be necessary to add a few items here on these two subjects, 
and to correct such errors as I have fallen into. 
Although the Curculio now infests the cultivated species of Plum ( Prunus domestica, 
Lmnaeus,) to fully as great an extent as our common wild species ( Prunus americana,) 
yet it is only at a comparatively recent date that it attacked our cultivated Plums, and 
since that epoch it has been growing every year worse and worse, and making on¬ 
slaughts upon other fruits such as the Peach, the Cherry, and even the Apple. “ Cur- 
culios,” said the Hon. D. J. Baker, in 1855, “ were unknown and never made their 
incursion into this region, until some years after the organization of our State Govern¬ 
ment,” A. D. 1818. ( Transactions Illinois State Agricultural Society , II. p. 48.) There can 
be little doubt, however, that Curculios have existed for time immemorial in our 
State, breeding in wild plums ; because, before tame plums and peaches and apricots 
were imported into this country from Europe, the insect must necessarily have bred in 
the wild plum, and wild plums are very abundant in Illinois, and moreover we know, 
from our present experience, that the climate of Illinois is quite congenial to the consti¬ 
tution of this insect. It would certainly, therefore, seem to follow that, in this as in so 
many other cases, when an insect has incidentally acquired a habit of feeding indiscrim¬ 
inately upon a different species of plants, to that upon which alone it naturally fed in 
the first instance, it transmits that habit by the laws of inheritance to its immediate 
descendants. When a race has once been formed, having such a habit, nothing seems 
more natural than that, under certain peculiar circumstances, such for instance as the 
absence of the original food-plant, another race should be very slowly and gradually 
formed, which exclusively attacks the new food-plant. If we suppose this second race 
to interbreed exclusively with itself, and to have thereby acquired, in a long series of 
ages, either a moral indisposition or a physical incapacity to interbreed w T ith individ¬ 
uals belonging to the original race, then it becomes almost as effectually isolated 
from the original race, as if it were separated therefrom by the Atlantic Ocean, or by 
such an insurmountable barrier as the Rocky Mountains. Now, we know that races of 
insects, and indeed of other animals as well, when separated from each other by such 
physical barriers, often run into what are technically termed “geographical races that 
is, come to differ constantly from each other in more or less slight peculiarities of size, 
form, or color. Hence it is but reasonable to suppose, that distinct races of some par¬ 
ticular insect, inhabiting the same geographical area, but feeding upon distinct plants 
and never interbreeding with each other, should also, in a long series of ages, come to 
differ from one another in size, form, or color. Such distinct races I have proved to 
have an actual existence in numerous cases, and have given them the name of “ Phyto- 
phagic Species.”* 
I by no means infer that, in the case of the Snout-beetle that infests our Plums, our 
* See my Papers on this subject in the Proceedings of the Entomological Society of Philadelphia , Yol. 
III. pp. 403-430 and Yol. V. pp. 194-216. 
