86 



by such physical barriers, often nm 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 particular 

 insect, inhabiting the same geographical area, but feeding upon dis- 

 tinct plants and never interbreeding wil:h 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 "Phytophagic 

 Species.'"* 



I by no means infer that, in the case of the Snout-beetle that in- 

 fests our Plums, our Peaches, our Cherries and our Apricots, such a 

 phenomenon has as yet occurred, and that the plum-feeding form is 

 a different species from the cherry-feeding form, and that again from 

 the peach-feeding form, and so on. There is no reason whatever to 

 think so. But there actually, in my opinion, does exist a "Phyto- 

 phagic species" of the common Curculio, which is uniformly one-half 

 larger and which in the larva state feeds, not upon stone-fruit or pip- 

 fruit, but upon green Butternuts and Walnuts (Juglans.) from the 

 former of which I bred two individuals August 13th. Of this peculiar 

 type of Curculio I sent specimens 6 years ago to our great North 

 American authority in the Order of Beetles, Dr. J. L. LeConte; and 

 he pronounced them to be mere varieties of the Plum Curculio. They 

 scarcely (liff'er from that insect in any other perfectly constant char- 

 acter than size;f and at first sight we might suppose, that the in- 

 creased size was caused merely by the Butternuts and Walnuts being 

 more nourishing and stimulating food than Plums and Peaches; and 



*See my Papers on this subject in the Proceedings of Ihe Entomological 

 Society of Philadelphia, Vol. Til. i-jj. 403—430 and Vol. V. pp. 194—216. 



•j-Q^here is, I believe, a slight, but perfectly constant colorational charac- 

 ter by which these two forms are distingnishable. The broad band behind the 

 polislied black'humps on the wing-cases is, in the large-sized nut-inliabiting 

 form, of a dingy white color with a few milk-white spots. In the small plum- 

 inhabiting form, this same band is of a bright ochre-yellow color, with more 

 or less milk-white spots, which last, however, never occupy more than one- 

 half of the ochre-yellow band. Moreover, I am informed by Dr. Hull, that 

 the larva of the large-sized form — with which he has long been familiar — oc- 

 curs with him in hickory-nuts having their shucks marked by the character- 

 istic crescent-slit, and that this larva '"penetrates to the kernel of the nut." 

 Whereas, as is well known, the larva of the small-sized form that frequents 

 the plum, never under any circumstances penetrates to the kernel of that 

 fruit. This difference in the habits of the two forms, is certainly very re- 

 markable. 



