322 Phylum Arthropoda 



broken if the pots are moved, the plants wilting as a result. In order 

 that the soil be kept fairly moist without becoming soggy; watering should 

 be more frequent in sunny or warm weather and less so in cool, damp 

 weather. When young and well watered, the plants have a very succulent 

 growth upon which aphids do well. On the other hand very young 

 plants of but two or three leaves may be injured by too heavy an infesta- 

 tion. It is well to plant about twice a week so the aphid population may 

 continually expand to plants of suitable size. It is also well to eliminate 

 the older, heavily infested plants gradually so the population will not 

 become too great and overrun the young plants excessively. The older 

 plants are less succulent and less attractive to migrating aphids ; colonies 

 developing upon them produce increased numbers of winged migratory 

 females. Furthermore, the older colonies are likely to become so para- 

 sitized by hymenopterous parasites that the entire aphid culture is in 

 danger of being affected. 



Other factors than moisture may influence the physiological activity of 

 the plant, thereby affecting the nature of the cell sap upon which the 

 aphids feed. In the heat of summer the greenhouse should be kept as 

 cool as possible and the plants shaded with cheesecloth or white-wash on 

 the glass overhead. In midwinter in the north it is difficult to keep aphids 

 in health because of the reduction of available daylight. 



In his tests of the toxicity of contact insecticides, Richardson used 

 undisturbed colonies of Aphis rumicis by cutting the leaves and plants 

 bearing them and inserting the stems through two-hole rubber stoppers in 

 small bottles of water. These bottles were then set on white paper and 

 surrounded by tanglefoot bands. Tattersfield used only adult wingless 

 parthenogenetic females, descended from a single female. The successive 

 generations were reared upon broad bean plants in pots. In order to 

 separate the desired individuals the plants were cut and allowed to wilt 

 slightly to make the aphids remove their stylets from the leaf tissue and 

 wander about. Then the insects were easily and safely handled with a 

 camel's hair brush. If the mouthparts were to remain inserted in the 

 leaf they might be injured when the aphids were brushed off. 



Bibliography 



Davidson, J. 1926. The sexual and parthenogenetic generations in the life-cycle 



of Aphis rumicis, L. Verh. Ill Internat. Ent. Kongr. Zurich, 1925, 2:452. 

 Franssen, C. J. H. 1927. Aphis fabae, Scop., en aanverwante soorten in Nederland. 



90 pp. Wageningen. (Abst. in Rev. Appl. Ent. 15:464, i9 2 7)- 

 Horsfall, J. L. 1925. The life history and bionomics of Aphis rumicis. Univ. 



Iowa Studies Nat. Hist., 11, No. 2, 57 pp. 

 Richardson, C. H., and Smith, C. R. 1923- Studies on contact insecticides. U.S. 



Dept. Agric, Dept. Bull. 11 60. 

 Tattersfield, F., and Morris, H. M. 1924. An apparatus for testing the toxic 



values of contact insecticides under controlled conditions. Bull. Ent. Res. 14:223. 



