Aphid infestations reduce monarch butterfly colonization, herbivory, and growth on ornamental milkweed

Mach, Bernadette Maria; Long, W. H.; Daniels, Jaret C.; Dale, Adam G.

doi:10.1371/journal.pone.0288407

Cited by 2 publications

(1 citation statement)

References 54 publications

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“…Parasite infection reduces monarch wing strength and flight capacity, contributing to migratory dropout (27,28). Second, concern about monarch decline has led to the widespread planting of non-native milkweeds such as Asclepias curassavica and Calotropis gigantea by homeowners and even land managers (29,30). These host plants maintain vegetative growth later into the fall than native milkweeds, and this can pull monarchs out of their migratory phase (31).…”

Section: Discussionmentioning

confidence: 99%

Dramatic Recent Declines in the Size of Monarch Butterfly (Danaus plexippus) Roosts During Fall Migration

Davis,

Croy,

Snyder

2024

Preprint

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The conservation status of monarch butterflies in North America is a topic of intense scrutiny and debate. It is clear that winter colonies in Mexico are declining, yet some recent studies suggest that summer breeding populations are relatively stable and similar to historical abundances. One possible explanation for these discordant patterns is that fall migration success has been recently disrupted. Here, we use a relatively unexplored citizen-scientist dataset on the size of monarch “roosts,” which are resting aggregations on vegetation, to infer changes in monarch abundance along the fall migration route over the last 17 years. We found that the timing of migration remained relatively unchanged while the flyway has generally become warmer and greener. Warmer and greener conditions were associated with larger roosts, yet we found steady, dramatic declines in roost sizes through time that were independent of climate and landscape factors. Roost sizes have declined as much as 80%, with losses increasing from north to south along the migration route. These findings suggest that failure during the fall migration could explain the apparent drop in monarch numbers from summer breeding to overwintering populations. This in turn suggests that conservation efforts that support fall migration success are most needed, such as limiting the planting of non-native milkweeds that enhance parasite loads and perhaps dampen migration success. Overall, it appears the fall migration of monarch butterflies is under imminent threat, even if the species’ overall survival is not.

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Section: Discussionmentioning

confidence: 99%

Dramatic Recent Declines in the Size of Monarch Butterfly (Danaus plexippus) Roosts During Fall Migration

Davis,

Croy,

Snyder

2024

Preprint

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Target and non-target effects of insecticide use during ornamental milkweed production

Mach,

Glynn,

Daniels

et al. 2024

Environmental Entomology

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There are widespread public efforts to conserve wildlife in urbanized landscapes via the installation of nursery-grown plants that support Lepidoptera taxa. Insecticides are commonly used during nursery production to suppress key plant pests, and many products have extended periods of toxicity and affect a wide range of herbivore taxa. While there are plentiful toxicological data on bee species, predominantly the Western honey bee (Apis mellifera L.), little is known about how insecticides affect nonpest lepidopterans. Lepidoptera has different modes of exposure (e.g., leaf-feeding) and differences in susceptibility to insecticide target sites compared to bees. Consequently, many products compatible with bee conservation pose an uncertain risk to nonpest lepidopterans and thus may represent an under-recognized conflict with conservation efforts. Using the monarch butterfly (Danaus plexippus, L.), tropical milkweed (Asclepias curassavica, L.), and oleander aphid (Aphis nerii, Fonscolombe, 1841) system, we conducted leaf and whole-plant feeding assays to evaluate effects of acute and chronic monarch exposure to industry standard and alternative reduced-risk insecticides used during nursery production. We also evaluated the efficacy of these insecticides against their target pest, the oleander aphid. Our results indicate that insecticides used to control pests on ornamental milkweed can cause monarch larval mortality up to 4 wk after treatment application. Furthermore, the duration of aphid suppression is often shorter than the duration of adverse effects on monarchs. This study demonstrates a conflict between insect pest management and Lepidoptera conservation during ornamental plant production and has implications for the conservation value of ornamentals after retail sale.

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Aphid infestations reduce monarch butterfly colonization, herbivory, and growth on ornamental milkweed

Cited by 2 publications

References 54 publications

Dramatic Recent Declines in the Size of Monarch Butterfly (Danaus plexippus) Roosts During Fall Migration

Dramatic Recent Declines in the Size of Monarch Butterfly (Danaus plexippus) Roosts During Fall Migration

Target and non-target effects of insecticide use during ornamental milkweed production

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