Aphid infestations reduce monarch butterfly colonization, herbivory, and growth on ornamental milkweed
Mach BM, Long W, Daniels JC and others. PloS one, July 2023.
Read the paper Free to read · doi:10.1371/journal.pone.0288407
What this paper is about
Ornamental milkweed in gardens and nursery stock often carries heavy oleander aphid infestations. The authors tested what that does to monarchs using the plant.
Monarchs laid on infested plants less, ate less, and grew less well on them. Gardeners are told aphids on milkweed do not matter; for the plant that is true, for the monarchs on it less so.
Summarised here from the abstract below. Not the authors’ words.
Abstract
Anthropogenic disturbance is driving global biodiversity loss, including the monarch butterfly (Danaus plexippus), a dietary specialist of milkweed. In response, ornamental milkweed plantings are increasingly common in urbanized landscapes, and recent evidence indicates they have conservation value for monarch butterflies. Unfortunately, sap-feeding insect herbivores, including the oleander aphid (Aphis nerii), frequently reach high densities on plants in nursery settings and urbanized landscapes. Aphid-infested milkweed may inhibit monarch conservation efforts by reducing host plant quality and inducing plant defenses. To test this, we evaluated the effects of oleander aphid infestation on monarch oviposition, larval performance, and plant traits using tropical milkweed (Asclepias curassavica), the most common commercially available milkweed species in the southern U.S. We quantified monarch oviposition preference, larval herbivory, larval weight, and plant characteristics on aphid-free and aphid-infested milkweed. Monarch butterflies deposited three times more eggs on aphid-free versus aphid-infested milkweed. Similarly, larvae fed aphid-free milkweed consumed and weighed twice as much as larvae fed aphid-infested milkweed. Aphid-free milkweed had higher total dry leaf biomass and nitrogen content than aphid-infested milkweed. Our results indicate that oleander aphid infestations can have indirect negative impacts on urban monarch conservation efforts and highlight the need for effective Lepidoptera-friendly integrated pest management tactics for ornamental plants.
Abstract reproduced from the published paper, which is licensed CC BY. Copyright remains with the authors.
Milkweeds in this paper
- Tropical Milkweed Asclepias curassavica
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title = {Aphid infestations reduce monarch butterfly colonization, herbivory, and growth on ornamental milkweed (listing)},
author = {{Milkweed USA}},
year = {2026},
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