Aphididae 321 



and shape desired. They may be ventilated by cutting any number and 

 size of openings in the side. They are very neat and smooth within, 

 making it easy to observe specimens at all times. 



J. G. N. 



THE NASTURTIUM APHID, APHIS RUMICIS 



H. H. Shepard, University of Minnesota 



KPHIS rumicis is used more as a test insect for determining the relative 

 l\ effectiveness of contact insecticides than for any other purpose. It is 

 the common black aphid, or plant louse, infesting nasturtium (Tro- 

 paeolum ma jus) and many other plants, and is known as the bean, dock, 

 or nasturtium aphid. Although this aphid is reported from many woody 

 and herbaceous plants, some of these do not seem to furnish suitable 

 food, for after a few generations the aphid leaves them for more favor- 

 able locations. In laboratory work in this country it has been reared 

 upon nasturtium plants, whereas in the work of Davidson and of Tatters- 

 field in England, the broad bean (Vicia jaba) was employed as its food. 

 There is some confusion regarding the number of species of aphids in- 

 cluded under the name A. rumicis (Franssen, 1927, and others). Hors- 

 fall has pointed out that there are two distinct types of life cycle; one 

 with woody shrubs as primary food plants on which the eggs are laid and 

 the first generations develop in the spring, the secondary food plants 

 being herbaceous; the other with primary food plants such as Cheno- 

 podium album and Rumex, and these and other herbaceous plants as 

 secondary food plants. 



There are several reasons why A. rumicis is to be preferred for the 

 purpose mentioned. The individuals are black and show up well on a 

 light background, resulting in less eye strain after counting large num- 

 bers of them than if a green species were employed. A. rumicis is short 

 legged and less likely to be injured in handling than the other species 

 which are long legged and more awkward. It moves more slowly when 

 disturbed by irritating chemicals, and hence is easier to keep within 

 artificial barriers. 



This species is easily reared in the greenhouse, reproduction being con- 

 tinuous throughout the year if favorable conditions are maintained. 

 Colonies may be started easily on young nasturtium plants by trans- 

 ferring to them a few aphids. The most important consideration is the 

 growth and condition of the nasturtium plants. The seeds of the dwarf 

 nasturtium, soaked in tepid water for an hour or so, should be planted 

 in rich black loam. For convenience in handling it is customary to plant 

 several seeds in a 3- or 4-inch flower pot and set the pots closely on the 

 surface of the soil in the greenhouse bench. However, after the plants 

 become of medium size the roots extend into the soil of the bench and are 



