336 ANNUAL OF SCIENTIFIC DISCOVERY. 



THIS POTATO DISEASE. 



AMONG the various causes assigned by different observers as to tho 

 origin of the potato disease, that of insects has been extremely common, 

 both in this country and in Europe ; but apparently without reason. 

 The following is the opinion of Dr. T. W. Harris, the eminent ento- 

 mologist of Harvard University, as given in a published letter, answer- 

 ing inquiries in relation to this subject. 



After adverting to various species of insects which have been 

 charged by various persons as the authors of the potato disease, viz., 

 the larvcB of Crioccris trilineata, the Coccinella, black-bugs and others, 

 Dr. Harris says : I could enumerate, at least, half a dozen more 

 kinds of insects that are occasionally or always to be found, in their 

 season, on the potato vines, insects varying in size from the minute 

 black Haltica and small bugs, to the big potato-worm, or Sphinx 

 quinquemacuta, all of them destructive according to the extent of 

 their powers, but innocent of the great offence, which might be charged 

 to them with as much propriety as to other insects, of causing the 

 potato disease. I will only advert to one more, namely, the Baridius 

 trinotatus, an insect for whose history we are indebted to a lady, Miss 

 Morris, of Germantown. In the larva state it lives in the stems of the 

 potato, where it is finally transformed to a little gray beetle, having 

 three black dots on its shoulders. This insect, though common enough 

 in the Middle States, I have never seen in New England, in the course 

 of 30 years of observation, and am confident that it must be rarely found 

 here, if at all. Miss Morris, when she first discovered its habits, 

 thought she had detected the real culprit, but has become convinced 

 that the potato-rot is not caused by it, though the ravages of this insect 

 are admitted to be very considerable. A. year or two after the potato 

 rot appeared in England, a Mr. Srnee thought he had discovered the 

 cause of it, in the attacks of certain plant-lice, or aphides, and he wrote 

 a work on the subject, and dedicated it to Prince Albert. British 

 naturalists, however, did not sustain him in his views. 



As the potato-rot had spread over Europe, and prevailed there to an 

 alarming extent, before it reached America, and as the disease found 

 here occurs with precisely the same symptoms and results as in Europe, 

 it must, wherever and whenever it appears, have one common specific 

 cause. If occasioned by insects, then the insects causing it must be of 

 the same kind or species in all regions where the disease has extended. 

 It would be entirely unphilosophical, and contrary to all analogy and 

 all experience, to attribute the disease to one kind of insect in one 

 country, and to an entirely different kind of insect in another country, 

 to aphides in England, to " black-bugs " in America, to lady birds in 

 Massachusetts, and to the Baridius trinotatus in Pennsylvania. It is a 

 well-established fact that the insects of America and of Europe are not 

 identical, excepting only in those few cases where some one species of 

 one country has been introduced, by the intervention of man, into the 

 other country. It has never been shown, and I think will never be 

 proved, that any one species of insect, of sufficiently destructive powers 

 to prove extensively injurious to the potato crop, is to be found alike 

 on the potatoes of Lurope and of America ; and, until such proof is pro- 



