Migratory tendency in aging populations of the pea aphid, Acyrthosiphon pisum

Sweep samples of the aphid, Acyrthosiphon pisum, were collected from six natural populations ranging in age from one to five years. Clones were established in the laboratory from the field-collected adults and tested for their migratory tendency in two subsequent generations by measuring the percentage of winged offspring produced in response to a standard stimulus. The number of aphids in sweep samples and the percentage of winged and wingless aphids were also determined. Tests on the first laboratory generation revealed a decline in migratory tendency with the age of the source population, but no such relationship was detected in tests on the second generation. These results are consistent with an explanation based on maternal age effects and differences in adult age structure among populations of different age. They are not consistent with one based on genetic differences among populations. Older populations also had higher densities and a lower percentage of alate adults. The percentage of larvae with wing buds was positively correlated with population density, but not population age.