1st Place: D3137: Direct and indirect effects of drought and host plant species on the oleander aphid (Aphis nerii)

Plants produce chemical defenses to protect against herbivory. Specialist herbivores can turn the tables on plants and sequester these defenses for use against their own natural enemies. Oleander aphids are specialists known to sequester toxic cardenolides from milkweeds. Production of cardenolides varies across milkweed species and may also be influenced by drought. The objective of this study was to assess the direct and indirect effects of drought on oleander aphid (Aphis nerii) performance and parasitism on three different milkweed (Asclepias) host species. We added aphids to well-watered or water-limited common (A. syriaca), swamp (A. incarnata), and tropical (A. curassavica) milkweed plants with parasitoid wasps (Aphidius colemani) present or absent and examined aphid population growth and parasitism rates. We found that the direct and indirect effects of drought on aphids depended on plant species, with population growth and parasitism higher on some species than others. Our results suggest that abiotic environmental change may impact interactions between oleander aphids, their host plants, and natural enemies.