New Study: Loss of milkweed linked to plummeting number of Monarch Butterflies
According to a new study conducted by Prof. Ryan Norris and doctoral researcher Tyler Flockhart and a team of Scientists at the University of Guelph in Ontario, Canada, the dramatic decline in the monarch butterfly population in eastern North America is due largely to the steady loss of milkweed crops in U.S. breeding grounds.
Scientists at the University of Guelph say it provides the first proof of the critical connection between the monarch's sole source food and the declining population. Having picked apart the various factors linked to the drop in monarch butterfly populations - including climate change and storms in the wintering grounds for Monarchs - the researchers confirmed their theory that the lack of milkweed is likely the principle culprit in the chain and new anti-weed treatments for farm land may be the leading agent of the change.
Although originally thought to be caused by other forces in the region of Mexico where the Monarchs winter after a long migration, there is evidence that Monarchs have been able to recover regularly from storm related events that wiped out as much as 80% of the population at once. But the interruption of the breeding cycle, which takes place in a broad swath of both the US and Canada, seems to be placing the species in real jeopardy.
"Milkweed loss specifically in the midwestern U.S. is likely contributing the most to monarch declines, but the loses of the food species are occurring everywhere that the plant grows" according to Flockhart. The study was published in the Journal of Animal Ecology.
The reason that the midwest seems to have the dominant effect is quite simply that it is the corn belt and new techniques for enhancing the growth of corn and limiting the species considered to be "weeds" are having unintended consequences.
The plant is both the food source and the nursery for the species because, in addition to consuming its leaves the insect lays its eggs on it. It is also the only group of plants that monarch caterpillars feed on before developing into butterflies.
"Reducing the negative effects of milkweed loss in the breeding grounds should be the top conservation priority to slow or halt future population declines of the monarch in North America."
The study's findings, which are based on a mathematical model that includes all known factors linked to the decline of the butterflies, challenge long-held beliefs that their population drop was due to the degradation of their wintering grounds in Mexico. Mexican authorities have taken action to protect the wintering grounds but this new twist indicates that the attention has been in the wrong place and that action in the US and Canada will be needed to halt the drift toward extinction.
The authors say the loss of milkweed crops is likely not the only cause of the butterflies' falling numbers, but they're calling on governments to restore milkweed habitats.
Mexico, the United States and Canada agreed in February to form a working group on the conservation of monarch butterflies, with discussions expected to include milkweed restoration but we should not wait for government to address these issues. We can start immediately by planting milkweed in areas where they will flourish but not be subject to agricultural interference and particularly to the use of genetically engineered crops.
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