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06-20-2024

Butterfly decline in American Midwest linked to insecticides 

The use of insecticides is a significant factor in the decline of butterfly populations in the Midwestern United States, according to a new study led by the Washington Department of Fish and Wildlife

The experts found that while habitat loss and climate change contribute to the decline, insecticides, especially neonicotinoids used on crop seeds, are the primary drivers. 

Focus of the study

“Mounting evidence shows overall insect abundances are in decline globally. Habitat loss, climate change, and pesticides have all been implicated, but their relative effects have never been evaluated in a comprehensive large-scale study,” wrote the researchers.

“We harmonized 17 years of land use, climate, multiple classes of pesticides, and butterfly survey data across 81 counties in five states in the US Midwest.” 

Decline in butterfly diversity

Based on their analysis, the experts linked insecticide use to an 8% drop in butterfly species diversity. These findings underscore the need for better pesticide use data to understand and address the decline.

The researchers observed that neonicotinoid-treated seeds had the most significant impact on butterfly populations, particularly affecting the monarch butterfly. 

“We show that the shift from reactive insecticides to prophylactic tactics has had a strong, negative association with butterfly abundance and species richness in the American Midwest,” noted the study authors. 

Understanding the causes of butterfly decline 

Reliable and comprehensive pesticide use data, especially for neonicotinoid seed treatments, is crucial to fully understand the causes of butterfly decline.

“We found community-wide declines in total butterfly abundance and species richness to be most strongly associated with insecticides in general, and for butterfly species richness the use of neonicotinoid-treated seeds in particular,” the authors reported. 

“This included the abundance of the migratory monarch (Danaus plexippus), whose decline is the focus of intensive debate and public concern. Insect declines cannot be understood without comprehensive data on all putative drivers, and the 2015 cessation of neonicotinoid data releases in the US will impede future research.”

“We have taken a large step toward pinpointing the cause of decades of butterfly declines. Of the three causes typically invoked, insecticides rise above climate and land use changes as the most negative factors,” they concluded.

Global butterfly decline 

Global butterfly populations are experiencing significant declines due to a combination of factors. 

Shrinking habitats

Habitat loss and degradation, primarily driven by urban development and agricultural expansion, have reduced the natural environments where butterflies thrive. 

Pesticides 

Pesticide use in agriculture further exacerbates the issue by directly killing butterflies and their larvae. 

Climate change 

Climate change also plays a critical role, as shifting weather patterns and temperatures disrupt the delicate life cycles of butterflies, affecting their migration, breeding, and feeding habits. 

Invasive species

Additionally, the spread of invasive species, including plants that alter butterfly habitats and predators that prey on them, contributes to their decline. 

Conservation efforts are essential to address these challenges and preserve butterfly populations for the future.

Impact of insecticides on butterflies 

Insecticides, designed to control pest populations, often have unintended consequences on non-target species like butterflies. These chemicals can be harmful to butterflies at various life stages, from larvae to adults. 

Acute toxicity 

When butterflies come into contact with insecticides, either through direct spraying or by consuming contaminated plants, they can suffer from acute toxicity, leading to immediate death or long-term health issues. 

Insecticides can disrupt the butterflies’ ability to feed, reproduce, and navigate, which diminishes their populations and affects biodiversity. 

Cascading effects 

Additionally, the reduction of butterflies can have cascading effects on ecosystems, as they are important pollinators for many plant species. 

The decline in butterfly populations due to insecticide exposure highlights the need for more sustainable pest management practices that protect these essential insects.

The study is published in the journal PLoS ONE.

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