72 



Observations on the various Insects 



literally covered and black with the winged females, sticking in 

 closely- packed phalanxes, and in that position they died by the 

 end of July or earlier — without killing any of the plants, to the 

 best of my knowledge. 



No one acquainted with cultivation will attempt to deny that 

 the plant-lice have the power to destroy a crop, — for instance, the 

 horse and broad beans were a light crop, and entirely failed from 

 the attacks of Aphis Fahce in many districts in 1847 ; but in that 

 very year the potatoes in gardens, where the Aphides were abun- 

 dant, proved sound crops ; whilst in 1848, where no Aphides could 

 be found, the tubers were worse than at any former period. 

 That Aphides will puncture the potato-leaves there can be no 

 doubt, and so incline them to wither ; but there is no proof of their 

 poisoning the sap and causing the rot. Indeed it is only when 

 plants are smothered with them, as we see beans, turnips, hops, 

 and roses occasionally are, that their presence causes any real 

 mischief, and then it simply arises from the local exhaustion pro- 

 duced by the abstraction of the sap from the leaves or young 

 shoots, and of course when the circulation is impaired and the cel- 

 lular tissue is deprived of its nourishment and dried up, the foliage 

 becomes spotted and withers ; but in no instance have I seen the 

 Aphides on the potatoes in sufficient numbers to destroy the crop, 

 or even to injure the produce. 



The economy of the Aphides has been so amply detailed in a 

 former volume,* that I shall now merely identify the species above 

 noticed. 



1. Aphis Rapae, Curtis, Journal of Royal Agric. Soc, vol. iii. 

 p. 53, pi. C, figs. 1, 2, 3. 



Having received so many different species from various corre- 

 spondents with the name of A. vastator, it is difficult to decide 

 which is intended for the authentic one ; but some which were 

 stated to be typical examples, and identical with those figured 

 and described by Mr. Smee, leave little doubt on my mind that 

 they are the same as the Aphis Rapce. 



2. A. Humuli, Curtis, Gardeners' Chron. for 1846, p. 405. 

 The winged specimens are exceedingly like A. Rapa in size 



and colour. 



3. A. Persicae, Morren, is very like the preceding species, but 

 it is rather larger, with much longer and slenderer ducts. In the 

 autumn of 1834 prodigious swarms of this species were carried 

 by a hurricane over many parts of Belgium. f 



4. A. Fabae, Scop, Journal of Royal Agric. Soc, vol. vii. p. 

 418, pi. R, figs. 21 and 22. 



* Journal of Royal Agric. Soc, vol. iii. p. 49. 



f Ann. Acad. Roy. des Sci. de Bruxelles, for Aug. 1836. 



