affecting the Potato-crops. 



71 



of animals and parasitic insects in the previous year, whose pro- 

 vince it would have been to keep within bounds these troublesome 

 enemies to man. 



If, however, the prevailing- disease amongst the potatoes cannot 

 be traced to the presence of insects, there is a large number of 

 species which prey upon, and undoubtedly injure to some extent, 

 the most healthy crops, and of these the history will now be given. 

 It will be better to divide them into those which affect the foliage, 

 and others which infest the roots, first in a sound, later in a dis- 

 eased state. 



Aphides, or Plant-lice. 



Many varieties of these insects are found upon the leaves of the 

 potatoes during the spring and summer months, indeed so long as 

 the foliage remains green and succulent. Their first appearance 

 depends upon the mildness of the weather, for when it becomes 

 cold they do not generate, or at any rate very slowly, so that the 

 species disappear; but if a plant be taken and protected in a 

 greenhouse or sitting-room, their economy is not interrupted even 

 in the winter, as one sees by the Pelargoniums being covered with 

 Aphides when they are neglected. I have at this time (January) 

 two tulips in a pot, the convoluted leaves swarming with Aphides, 

 allied to the one infesting the peach-trees : the apterous females 

 are daily bringing forth young, and the pupae are hatching and 

 producing winged females.* But to return : I very much doubt 

 if there be any species exclusively attached to the potato, for the 

 one named Aphis vastator by Mr. Smee appears to me to be 

 identical with my A. Mapce, which inhabits turnip-leaves, and 

 was described and figured in this Journal in 1842, f 



In confirmation of my views I may state that, in April, Mr. 

 F. J. Graham has detected the Aphis Persicm J upon the potato- 

 leaves in his vinery ; the beginning of May, Mr. Denham found 

 A. granarius, or an allied species, in some abundance on the 

 potato-leaves at Broxmouth Park. On the 5th of June, 1847, I 

 observed upon my potato-haulm the hop-fly {Aphis Humuli) and 

 the turnip-plant louse {A. Rapoi) ; on the 13th also a species 

 without honey-tubes ; on the 17th several belonging to a group 

 separated from Aphis, and called Schizoneura ; and in July, Aphis 

 Fabce, the broad-bean louse, was in some force upon the potatoes, 

 whilst it was swarming upon other vegetables and garden flowers ; 

 for instance, the shoots of dahlias, the underside of the leaves of 

 the convolvuli, French and scarlet beans, beet, and parsnips were 



* Mr. F. Walker considers they are the A. vastator of Smee. 



t Vol. iii. p. 53, pi. C 5 f. 1, 2, 3, and Gardeners' Chron., vol. vii. p. 21. 



% Curtis's Guide, Genus 1047, where nearly sixty species are arranged. 



