Abstract
When reared in crowded conditions, 2nd generation individuals of the sycamore aphid were smaller and had a longer aestivation than when reared in isolation. The duration of the aestivation was further lengthened if their mothers were reared in crowds, but the influence of maternal crowding was not mediated by a plant factor since the 2 generations were reared on different sets of plants. The importance of maternal crowding and aestivation in the population dynamics of the sycamore aphid is discussed.