Fifty-two lines ofAcyrthosiphon pisum(Harris), the pea aphid, from three Australian locations did not produce oviparae and only one female produced males when reared at short photoperiods and low temperatures. We conclude that sexual reproduction is not common among Australian pea aphids. Fundatrix-like aphids with short appendages were collected from field populations in the spring. These were not true fundatrices, because it is unlikely that they hatched from sexually produced eggs. Samples of aphids from lucerne (alfalfa) showed that the relative length of appendages increased through the spring and early summer and decreased in the late summer and early autumn. When reared at room temperature with a long photoperiod, the offspring of fundatrix-like aphids had longer appendages than their parents and the length of the appendages increased in succeeding generations. Aphids reared at low temperatures with short photoperiods from before birth had reduced appendages. We conclude that environmental factors can affect the relative length of appendages in anholocyclic populations of the pea aphid.