Influence of host plant on oligophagous and polyphagous aphids, and on their obligate symbiont titers

Herbivorous insects show varying levels of diet specialization. Hemipterans usually feed on nutritionally poor diets, and harbor symbionts that supply the host with essential nutrients. Here, we investigate the effects of host plant suitability on the biology of the oligophagous aphid Aphis citricidus (Hemiptera: Aphididae) and the polyphagous Aphis aurantii (Hemiptera: Aphididae), and on their obligate symbiont Buchnera aphidicola. We investigated aphids development when restricted to host plants with different nutritional qualities, e.g. sweet orange (Citrus sinensis) and orange jasmine (Murraya paniculata) and when alternating host plant quality during the immature and adult stages. Sweet orange was the most adequate host for both aphid species, while orange jasmine had a much stronger impact on fitness for the oligophagous than for the polyphagous aphid. The growth pattern of Buchnera differed between aphids and host plants. Buchnera density increased as A. citricidus developed on sweet orange, but decreased in A. citricidus feeding on orange jasmine. Buchnera increased in density in A. aurantii on both host plants. Finally, these fluctuations in Buchnera density reflect the contribution of food source, and we provide arguments on the dynamics of the interactions among aphids, Buchnera and host plant suitability, considering the oligophagous-polyphagous dichotomy.