70 



Observations on the various Insects 



IV. — Observations on the Natural History and Economy of various 

 Insects affecting the Potato-crops, including Plant-lice, Plant- 

 hugs, Frog-flies, Caterpillars, Crane-flies, Wireworms, Milli- 

 pedes, Mites, Beetles, Flies, Sfc. By John Curtis, F.L.S., 

 Corresponding Member of the Imperial and Royal Georgofili 

 Society of Florence ; of the Academy of Natural Sciences of 

 Philadelphia, &c. 



Paper XV. 



The disease* which has assailed the potatoes for the last four 

 years, frequently rendering the crop worthless, and setting human 

 ingenuity at defiance to discover a remedy, appears to result from 

 atmospheric influence, produced probably by a succession of cold, 

 heat, and unusual humidity, which did not agree with the consti- 

 tution of this imported esculent. Amongst the numerous causes 

 that have been assigned for the appearance of this alarming and 

 severe visitation, insects have been frequently taxed as the destruc- 

 tive agents, but I am convinced the calamity is not to be attri- 

 buted to their presence. f It certainly was remarkable that the 

 Aphides should have swarmed in countless myriads in 1847, but 

 the malady was not then so bad as it was in the previous and suc- 

 ceeding years, which appeared to me to be the most fatal to the 

 potato-crops, \ yet, as far as my observations extended, the plant- 

 lice were so scarce during 1846 that it was with difficulty I could 

 find specimens, and I did not see a single Aphis upon my pota- 

 toes in 1848, notwithstanding the crop was worse than it had ever 

 been before in my neighbourhood, more than half of them being 

 rotten. The appearance of the Aphides in such unprecedented 

 swarms may fairly be attributed to the same cause as the potato 

 rot — namely, certain conditions of the atmosphere, for it is gene- 

 rally admitted that the appearance of a species of insects in un- 

 usual abundance, may be the effect either of some exciting influ- 

 ence, as electricity, or of a congenial temperature,, creating a 

 climate favourable to the increase of the animal, such as heat and 

 moisture. In other instances it no doubt is owing to the absence 



* Murrain, being " a plague in cattle," ought never to have been 

 applied to the potato disease, as it frequently has been. 



f M. Guerin holds a similar opinion, as well as Mr. Westwood and 

 different members of the Entomological Society of London. Vide Bulletin 

 of the Royal and Central Society of Agriculture in Paris, vol. v. p. 331, and 

 Gardeners' Chron., vol. viii. p. 468. 



% The very great breadth of potatoes planted in 1848 has given so much 

 larger an amount of produce, that the loss from disease is not felt as it would 

 have been had the usual quantity only been grown ; and this is a very 

 important fact to keep in view as regards our future prospects. Indeed, is 

 it worth while, at present at least, to sacrifice so many acres of valuable 

 land in growing rotten potatoes ? 



