Years ago, the seed companies blasted a USDA researcher after I wrote a No-Till Farmer item stating that Bt corn could reduce butterfly populations. While there has been plenty of controversy over the years on whether pollen from Bt corn is toxic to butterflies, later research demonstrated that criticism of the researcher’s findings was not justified.

In 1999, the relationship between monarch butterflies and Bt corn was confirmed when a Cornell University study indicated that Bt corn pollen could poison monarch butterfly larvae. Leading to a public outcry in Europe against biotech corn, these findings led to calls from environmental groups to slow the spread of gene-altered crops.

Even though pollen from Bt corn can be toxic to butterflies, the risk is extremely low. In fact, data from several research studies estimates that pollen from Bt corn kills less than 0.05% of monarch butterflies in the Midwest each summer.

Billions Down to Millions

But with a serious decline in monarch butterfly numbers, in 2022 the International Union for the Conservation of Nature (IUCN) added the migratory monarch butterfly to its endangered and threatened species list. This decision was based on data showing that while there were as many as 1 billion monarchs on the planet in the 1990s, these numbers have dropped to only around 33 million in 2022.

This sharp decline in the monarch butterfly population could lead to trouble among all pollinator species, such as butterflies and bees. The Center for Biological Diversity describes the decrease in monarchs as a "harbinger of widespread environmental change." It’s important as 35% of the world’s crops depend on effective pollination.

The IUCN maintains logging and deforestation for urban development and agricultural use has destroyed much of the butterflies winter shelter in California and Mexico. At the same time, extensive use of herbicides has eliminated milkweed in many fields, which is the no. 1 source of food for butterfly larvae.

Endangered Candidate

While the federal government’s U.S. Fish and Wildlife Service does not officially list the monarch butterfly as an endangered species, it has listed it as a possible candidate. 

Despite the latest research findings, biotech critics still maintain there’s not enough data about Bt corn to be sure it is safe for butterflies. Yet other data supports the fact that no-tillers don’t need to be concerned about reducing monarch butterfly populations when planting Bt corn.