Reproductive adaptation in alate adult morphs of the English grain aphid Sitobion avenae under starvation stress

Adapting their reproductive physiology is a tactic that insects use in responding to conditions of food unavailability. The present study examined the potential effects of starvation periods on the ovarian development and reproduction of alate adult morphs of Sitobion avenae (Fabricius). Morphs both continuously fed and starved aphids contained two telotrophic ovaries, each comprising five ovarioles. As time increase after emergence, the number of offspring produced by the fed aphids increased gradually, whereas the number of embryos in their ovaries decreased gradually. Both the number of mature embryos and the volume of embryos rapidly increased at 24 h after emergence, and then remained at an approximately constant level between 24 and 144 h. Compared to the fed aphids, starved aphids only produced a small number of nymphs, and there was no significant change in the total number of embryos between 24 and 144 h, whereas both the number of mature embryos and volume of embryos increased significantly. Irrespective of starvation period, highly significant relationships between life span and fecundity were found. Adult aphids starved for longer periods presented lower longevity and fecundity, but dead females contained more mature embryos than those starved for shorter periods. These results suggested that, under starvation stress, S. avenae tends to invest in the development of larger embryos at the expense of reducing lifespan and future fecundity. This adaptive reproductive strategy under starvation stress could be one of the factors contributing to the successful establishment of new colonies of alate migratory aphids.