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Fred T. Davies Jr., Chunajiu He, Amanda Chau, Kevin M. Heinz, and Andrew D. Cartmill

This research details the influence of fertility on plant growth, photosynthesis, ethylene evolution and herbivore abundance of chrysanthemum (Dendranthema grandiflora Tzvelev `Charm') inoculated with cotton aphids (Aphis gossypii Glover). We tested five fertility levels that consisted of 0%, 5%, 10%, 20%, and 100% (375 ppm N) of recommended nitrogen levels. Aphid abundance was greatest at high fertility. Fertility affected the vertical distribution of aphids. A higher population of aphids were observed in physiologically mature and older leaves at low fertility, whereas at high fertility young leaves had 33% more aphids than older, basal leaves. Aphids depressed plant vegetative and reproductive growth, and altered carbohydrate partitioning at high fertility. Aphid-inoculated (AI) plants at high fertility had increased specific leaf area [(SLA), i.e., thinner leaves] and greater leaf area than aphid-free (NonAI) plants. Aphids caused greater ethylene production in reproductive buds and young leaves of high fertility plants, but had no effect on ethylene evolution in physiologically mature or older, basal leaves. Plant growth, leaf nitrogen (N), phosphorus (P), iron (Fe) and manganese (Mn) increased at higher fertility, as did chlorophyll and photosynthetic rates. Leaf N was highest in young and physiologically mature leaves compared to basal leaves. Aphids decreased leaf N and P. Aphids reduced photosynthesis in young leaves of high fertility plants, whereas physiologically mature and older leaves were unaffected.