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Cornell researchers find glyphosate herbicide unlikely source of Monarch butterfly decline

| | April 26, 2016
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Photo by Tony Hisgett
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In the face of scientific dogma that faults the population decline of monarch butterflies on a lack of milkweed, herbicides and genetically modified crops, a new Cornell University study casts wider blame: sparse autumnal nectar sources, weather and habitat fragmentation.

“. . . [W]e have pieced together the monarch life cycle to make inferences about what is impacting the butterflies,” said Anurag Agrawal, Cornell University professor of ecology and evolutionary biology and senior author on the new paper, to be published April 25 in the journal Oikos.

. . . .The study finds that a “lack of milkweed, the only host plant for monarch butterfly caterpillars, is unlikely to be driving the monarch’s population decline, as the problem appears to occur after they take flight in the fall,” said Agrawal.

. . . .

. . . .Yes, said Agrawal: “The consistent decline at the overwintering sites in Mexico is cause for concern. Nonetheless, the population is six times what it was two years ago, when it was at its all-time low.” Agrawal credits the population rebound to improved weather and release from the severe drought in Texas.

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Agrawal said that a persistent decline caused by lack of nectar sources or other threats such as habitat loss or insecticide use can conspire with large annual population fluctuations – mostly due to weather – and may eventually push monarchs to dangerously low numbers.

“Given the intense interest in monarch conservation, the blame being put on herbicide use and the national dialog about potentially listing monarchs under the endangered species act, we have to get the science right,” said Agrawal.

Read full, original post: Beyond milkweed: Monarchs face habitat, nectar threats

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