Aphididae 325 



from seed at any time of year. Among these are beans, peas, cabbage, 

 radishes, tomatoes, nasturtiums, calendulas, and asters. Wheat and oats 

 are also useful. Each of these is accepted by some of the cosmopolitan 

 species, and some of them are the favored food of certain species. The 

 most convenient plants for experiments are those which grow rather 

 slowly. If a group of aphids is to be left on one plant during its entire 

 reproductive period of several weeks, the food plant should not become 

 unmanageable in that time. Calendulas and cabbage are among the best 

 of the plants named, in this regard, but are not always the most favorable 

 to aphid growth. If more rapidly growing plants are used, the aphids 

 may need to be transferred to fresh plants at intervals. 



Seeds should be planted, not in the pots with which the experiments are 

 to be conducted, but in seed plats. The young seedlings should be trans- 

 planted to very small pots, and, when they are satisfactorily established 

 in these and begin to grow actively, should be removed, soil and all, 

 without disturbing their roots, to the larger pots to be used in the experi- 

 ments. 



The common potato is suitable for cosmopolitan species, and is like- 

 wise the host of species peculiar to it. The plants may be furnished in 

 quantity the year round, but one must look ahead. New potatoes re- 

 quire 6 or 8 weeks of rest before they will sprout. Through the winter, 

 any potatoes harvested in the fall may be counted on to sprout fairly 

 promptly. Old potatoes planted later than May, however, especially 

 indoors, are likely to produce a proportion of unhealthy plants. Hence it 

 is better to begin to obtain new potatoes (shipped in at first from warmer 

 regions) at least as early as March, and periodically thereafter through 

 the summer and fall, so that a supply capable of sprouting is always on 

 hand. There are ways of hastening the sprouting of potatoes, [See foot- 

 note on p. 328.] but none of them is superior to the method of allowing 

 time for rest, which requires only foresight. The soil used for any plants 

 should be renewed occasionally, and pots should be cleaned. 



Aphids which in nature ordinarily alternate between two host plants 

 may often, perhaps usually, be induced to live indefinitely on one of 

 them. The most extensive experiments yet done with aphids concerned a 

 species that alternates irregularly between rose and potato. It would 

 be difficult to use the rose in experiments, but potato plants were found 

 to suffice. 



In general, aphids should be placed on a plant while it is still very 

 small, and be allowed to accumulate while the plant grows. Since most 

 aphids wander on slight provocation, they must be confined. Lantern 

 globes closed at the top with voile or cheese cloth are suitable. The pots 

 for the plants should be large enough to let the lantern globe rest on the 

 soil, thus making an aphid-tight seal of the enclosure. Water for the 



