It is the loss of breeding grounds in the United States, not necessarily the wintering grounds in Mexico that is the cause of recent and projected population declines of migratory monarch butterflies in eastern North America, reveals a new study by scientists at the University of Guelph in Ontario, Canada.
The research showed that it is the decline in the growth of milkweed, the only group of plants that monarch caterpillars feed upon that is partly to blame. Changes in milkweed abundance in their breeding areas can affect everything from larval competition for food to egg-laying in adults.
Industrial farming contributed to a 21 per cent decline in milkweed plants between 1995 and 2013, and much of this loss occurred in the central breeding region, the study said.
"The continuing rapid loss of milkweed projected for this region, attributable to land cover changes and shifts in agricultural practices, is a very large concern," said lead author Tyler Flockhart.
If left unchecked milkweed loss will cause the monarch population to decline by at least another 14 per cent in the coming years, the study reported.
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