Alfalfa cyclitols in the honeydew of an aphid

The free cyclitols pinitol, ononitol and myo-inositol occur in the honeydew (excreta) of pea aphids (Acyrthosiphon pisum) which feed on pea aphid-susceptible alfalfa (Medicago sativa cv Caliverde). These cyclitols also occur in the leaves and stems of alfalfa. Aphids were incapable of de novo synthesis of these cyclitols. Honeydew production by the pea aphid results from ingesting phloem-sap, so the occurrence of cyclitols in honeydew results from their translocation in the phloem. The relatively high content of myo-inositol in honeydew indicates that it is selectively translocated. The most abundant alfalfa cyclitol, pinitol, had no effect on aphid feeding behavior at concentrations up to 1% (w/v; artificial diet).