New research points to culprit in Monarch Butterfly Die-Off
A mass die-off of monarch butterflies in Southern California last year has been traced to a likely source: widely used pesticides. New peer-reviewed research published in Environmental Toxicology and Chemistry provides compelling evidence linking chemical exposure to the deaths of hundreds of monarchs near the Pacific Grove Monarch Sanctuary, according to The Guardian.
The butterflies were found dead or dying in clusters in January 2024, showing signs of neurotoxic poisoning—such as twitching and disorientation. Laboratory tests on ten of the specimens revealed each had been exposed to seven different pesticides. Among them were three types of pyrethroids, a class of insecticide commonly used in both agriculture and home landscaping throughout the state.
Researchers believe the contamination may have come from nearby residential pesticide use, which is often less strictly regulated than agricultural applications.
“This incident offered a rare, real-world window into how pesticides are affecting monarchs,” said Staci Cibotti, lead author of the study and a researcher with the Xerces Society for Invertebrate Conservation.
Monarch butterfly populations across North America have declined by roughly 90% since the 1980s, according to Environmental Health News. The species is currently being considered for protection under the Endangered Species Act.
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