The regulation of sodium, potassium and chloride in an aphid subjected to ionic stress.

The aphid Myzus persicae has been cultured on the sea aster, Aster tripolium , which was grown in fresh water or sea water nutrient medium. Samples of sieve tube sap, obtained through the severed stylets of feeding aphids, haemolymph, and honeydew were analysed for sodium, potassium and chloride content. On fresh water plants the blood sodium level of the aphids was found to be exceptionally low. At 0·2 mmol 1−1 it is the lowest recorded sodium concentration in the blood of any animal. The result is discussed in relation to the functioning of the insect's nervous system. Under the sea water condition all three ions are maintained in the blood at levels below those found in the imbibed or excreted fluid.