Effects of ant-attendance on the honeydew excretion and larviposition of the cowpea aphid, Aphis craccivora Koch.
The rates of honeydew excretion and larviposition were examined individually in apterous viviparous females of Aphis craccivora Koch on ant-free and ant-attended potted cowpea (Vigna unguiculata) plants. The ants used in these experiments were Iridomyrmex glaber (Mayr). The individual acts of honeydew excretion were recorded by observing the angle made between the body of the aphid and the leaf surface, since while excreting honeydew, the aphid raises the abdomen in the air. It was found that the frequency of honeydew excretion averages 0.86/h for ant-free aphids and 6.1 for ant-attended ones. There was little difference between the 2 groups in the frequency of larviposition (0.75 and 0.85/h, respectively). The mean interval between honeydew dropping was 32 min in ant-free colonies, as compared with 9.9 min in ant-attended ones. The angle of the honeydew excretion pose was significantly different for ant-free and ant-attended aphids. A higher angle appeared to facilitate concentration of the honeydew, increasing its viscosity, and also made it easier for the aphid to disengage the excretion from the anus with the hind legs.