Both Mexico and the United States are contributing to the potential extinction of the monarch butterfly despite the creation of a biosphere reserve to protect them.

The amazing feat of monarch butterfly (Danaus plexippus) migration from Mexico to the US and Canada is under threat from both directions. In Mexico habitat loss within the Monarch Butterfly Biosphere Reserve has become critical and in the US genetically modified cornfields shed pollen containing Bacillus thuringiensis (Bt), which can be fatal to the butterflies.

Deforestation in Mexico’s Monarch Biosphere Reserve

Illegal logging within the Monarch Butterfly Biosphere Reserve is the greatest threat to the butterflies in Mexico. Clear cutting results in stronger winds and colder temperatures in areas where the monarch butterflies winter. With millions of monarchs lost to exposure in the past couple of years, reforestation of nearly half of the biosphere reserve will be needed.

Monarch Habitat Loss and Pesticide Use in the US

But habitat loss is not confined to Mexico. In the US urban sprawl is dramatically affecting available habitat for monarch butterflies. Herbicide use to control growth along roadsides where milkweed had been a common species has reduced food sources for the butterflies at a point in the migration where nutrition is critical.

Pesticide exposure is another issue. In a study on DiPel, an insecticide containing Bt toxin, it was shown that monarch butterfly larvae exposed to DiPel all died, even 48 hours after application. Daily watering of the plants during the study period did not reduce the death rate.

GM Crops and the Monarch Butterfly

Also of significant concern is the increase in genetically modified crops, especially corn and soybeans, within the monarch butterfly breeding range. These GM crops are designed with that same Bacillus thuringiensis (Bt) toxin in them. The butterflies feed on the milkweed growing in the GM cornfields at the time when the corn is shedding pollen. That pollen is laden with Bt toxin.

This is of particular concern for the northern reaches of the monarch butterfly migration route. Ontario, Minnesota and Wisconsin have the highest percentage of larvae in GM cornfields at the time when pollen is being shed.

Helping the Monarch Butterfly to Survive

In Mexico, reforestation efforts are underway, with the World Wildlife Fund (WWF) leading efforts within the Monarch Butterfly Biosphere Reserve. Involving local communities in protecting the butterfly and its habitat is one way of helping the species. Creating a model sustainable tourism project with the monarchs as the centerpiece is another part of WWF’s approach to the problem.

GM crops are banned in many countries. It isn’t just butterflies that are affected by them. In the effort to rid crops of insect pests and competition from weeds, food supply and habitat for many other insects and birds are being lost. Given the increasing knowledge of the downside of these crops, it seems logical to push for a worldwide ban on them.

How Individuals Can Help

This is one situation where people can do something to help. Planting butterfly gardens increases habitat for these endangered insects. Milkweed is essential for the larvae so tolerance, or better yet encouragement, of this plant will help ensure new generations of monarch butterfly survive.

Other Endangered Butterflies:

Sand Mountain Blue and El Segundo Blue Butterflies

Checkerspot Butterfly