Larval pesticide exposure impacts monarch butterfly performance
Olaya-Arenas P, Hauri K, Scharf ME and others. Scientific reports, September 2020.
Read the paper Free to read · doi:10.1038/s41598-020-71211-7
What this paper is about
Monarch larvae were raised on common milkweed treated with six pesticides: an insecticide, two herbicides and three fungicides, each at the average and the maximum concentrations reported from field surveys.
The decline is usually attributed to milkweed loss from herbicide-tolerant crops. This tests whether residues on the milkweed that remains are also doing damage.
Summarised here from the abstract below. Not the authors’ words.
Abstract
The long-term decline of monarch butterflies has been attributed to loss of their milkweed (Asclepias sp.) host-plants after the introduction of herbicide-tolerant crops. However, recent studies report pesticide residues on milkweed leaves that could act as a contributing factor when ingested as part of their larval diet. In this study, we exposed monarch larvae to six pesticides (insecticide: clothianidin; herbicides: atrazine, S-metolachlor; fungicides: azoxystrobin, pyraclostrobin, trifloxystrobin) on their primary host-plant, A. syriaca. Each was tested at mean and maximum levels reported from published analyses of milkweeds bordering cropland and thus represent field-relevant concentrations. Monarch lethal and sub-lethal responses were tracked over their complete development, from early instar larvae to adult death. Overall, we found no impact of any pesticide on immature development time and relatively weak effects on larval herbivory or survival to adulthood. Comparatively stronger effects were detected for adult performance; namely, a 12.5% reduction in wing length in response to the fungicides azoxystrobin and trifloxystrobin. These data collectively suggest that monarch responses to host-plant pesticides are largely sublethal and more pronounced in the adult stage, despite exposure only as larvae. This outcome has important implications for risk assessment and the migratory success of monarchs in North America.
Abstract reproduced from the published paper, which is licensed CC BY. Copyright remains with the authors.
Milkweeds in this paper
- Common Milkweed Asclepias syriaca
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title = {Larval pesticide exposure impacts monarch butterfly performance (listing)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/research/larval-pesticide-exposure-impacts-monarch-butterfly-performance-2020/},
note = {Accessed DATE}
}