140 Food Plants of Aphis rumicis 



heavy infestation. On many other plants, however, although aphids 

 were present, the colonies were small. The individuals looked healthy 

 and happy, but the numbers produced were small, and the plants really 

 never became heavily infested. 



This would seem to show that the cell sap of certain plants affords 

 a suitable stimulus for certain species of aphids, resulting in rapid 

 reproduction of young, while on some other plants, although the cell 

 sap may afford a suitable food for the specific aphids, the stimulus 

 derived from it does not induce such a rapid reproduction of young. 



There is the question that the quality of the sap in any particular 

 species of plant may be subject to change according to the soil conditions 

 in which it may be growing. I have not any particular reference to 

 hand, but I believe work has been done, showing that by treating 

 certain plants with chemical substances they may be rendered immune 

 to a specific fungus attack. Mangolds and Beet have been recorded 

 from time to time, both in this country and in France and Germany, 

 as subject to infestation by Aphis rumicis. In some seasons, on the 

 other hand, these plants may be more or less free from infestation. 



In connection with this point, there seem to be two points for 

 consideration. Firstly, whether the presence in the neighbourhood of 

 these crops of food plants for which Ajjhis rmtiicis shows preference, 

 afforded sufficient food for the aphids and so prevented an overflow 

 to the Mangolds and Beet. Secondly, whether any special manurial 

 treatment of the soil rendered the crop more susceptible to attack. 



It would be interesting during such an outbreak, to tabulate the 

 food plants found in the immediate neighbourhood. It does not seem 

 at all unfeasible that in a very bad season, a " catch crop " might be 

 sown ; for example with Aphis rumicis, the aphids evidently prefer 

 Broad Beans and Poppies if these plants are present. 



Malanquin and Moitie (1913)^ record heavy attacks of Aphis papa- 

 veris in 1911 on the Sugar and Cattle Beet in the North of France. 

 They record the presence of the Aphis also on Spinach, Rhubarb, 

 Poppies and Beans. These authors add that this Aphis leaves the 

 seed plants about the middle of July because they do not afford sufficient 

 food and go to the Sugar and Cattle Beet. 



Davis {op. cit. p. 132) observed with Aphis maidi-radicis that when 

 food supply was scarce, the tendency was for winged forms to be 

 produced. 



^ Malanquin, A. and Moitie, A. (1'J13), " Le Pucciou dc la buttcrave dans le nord de 

 la Franct,'," La Vie Agricok, II, No. 24, pp. OU6-(5'J!). 



