Effects of the ant, Lasius Niger L., on the feeding and excretion of the bean aphid, Aphis Fabae Scop

1. To test the idea of Herzig (1937) that the excretion and feeding rates of aphids are stimulated by attendant ants, bean plants (Vicia faba), on which groups of nymphs of Aphis fabae were feeding, were made radioactive with 32P in water culture, so that the aphids took up the isotope and excreted it in their honeydew. The radioactivity of the honeydew taken from them by attendant Lasius niger was then compared with that of the honeydew excreted concurrently by unattended control aphids on separate plants. 2. By increasing their uptake of plant sap the ant-attended aphids produced twice as much radioactivity in their excreta as did the ant-free aphids. 3. The aphids directly control their rates of excretion and feeding, which are not determined solely by forces within the plant. 4. The aphid apparently controls its feeding by the ‘sucking pump’ in its head. It is suggested that the pump is normally closed but that periodically it opens to admit sap into its lumen and then closes ventrally to force the ingested sap into the stomach. During normal feeding the pump probably opens and closes at regular intervals; but when the aphid is ant-attended it could operated more frequently so as to force sap into the stomach more often. The uptake of sap by normally feeding aphids is apparently not continuous.