News

Loss of milkweed means loss of Monarchs

A new study says the loss of habitat in the United States, not wintering grounds in Mexico is the reason for the significant decline in Monarch butterfly population. The study from a research team at the University of Guelph in Ontario says the loss of milkweed especially in the cornbelt has been the culprit. Monarchs lay their eggs only on milkweed and when the caterpillars hatch they feed only on milkweed. Most of the milkweed is in agricultural areas where it is susceptible to herbicides. Professor Ryan Norris says from 1995 to 2013 there was a 21 percent reduction in milkweed in the Midwest.

Changes in milkweed abundance can affect everything from larval competition for food to egg-laying in adults. Lead author of the study, Tyler Flockhart says, “Left unchecked, milkweed loss will cause the monarch population to decline by at least another 14 per cent.” The researchers say, “Planting milkweed in the Central and Southern U.S. would provide the largest immediate benefit.” The study is published in the latest Journal of Animal Ecology

Up to now, the loss of winter habitat in Mexico was thought to be the main reason for the decline. Monarchs from the central and eastern United States spend winters in close concentration in the fir trees of the trans volcanic mountains in central Mexico. Because they are so concentrated, thousands in each tree, they are counted by the area covered. In a report last January, The World Wildlife Fund and Mexico’s Environmental Department cites as an example an area west of Mexico City which covered 1.65 acres this year compared to 2.92 acres last year and a peak of 44.5 acres in 1996.

AUDIO: Flockhart talks about the study 6:51 mp3

Read more from the University of Guelph here: