Bt corn may kill monarch butterflies

Travis Whittington

ISU researchers recently discovered that pollen from genetically enhanced corn possibly could kill monarch butterflies. A research study about the corn by two ISU entomologists was published in the Aug. 19 Internet version of an ecology journal called Oecologia. The study revealed that monarch butterflies can die simply by ingesting pollen from Bacillus thuringiensis (Bt) corn. Bt corn is a plant that has insecticidal toxins designed to kill corn bores. John Obrycki, professor of entomology, and graduate assistant Laura Hansen Jesse conducted the two-year experiment that began in May 1998. “We planted Bt corn and placed potted milkweed plants varying distances from the edge of the Bt corn field to capture actual pollen dispersal,” Obrycki explained. “The milkweed leaves were taken into a lab, and monarch butterfly larvae were then applied to the leaves. Larvae were also placed on milkweed leaves that had been exposed to pollen from corn that had not been genetically tampered with.” The study’s results showed that the monarch butterflies exposed to the Bt corn’s pollen had far higher mortality rates. “For two days, the larvae were exposed to the plants,” Obrycki said. “The larvae exposed to the Bt corn pollen showed a 20 percent mortality rate, while the mortality rate for the other larvae was zero. “In addition, some more leaves with the Bt pollen were washed off and checked with a dissecting microscope to make sure all the pollen was off,” he said. “Some larvae were then fed these leaves, and they attained a 3 percent mortality rate.” Even with the high mortality rates, many people in the transgenic crop industry have found this study to be inconclusive. “The study only focuses on one factor in a lab setting,” said Jerry Harrington, North American public relations manager for Pioneer Hi-Bred. “If monarch butterflies are to die in a field, many more factors have to take place. For example, pollen shed must be high in one area, larvae have to be present, and the larvae must chose to feed on a plant with pollen. “The Iowa State experiment was a field experiment that went into the lab,” he said. “The larvae were not given a choice of what to feed on in the lab. The larvae were simply put on a plant leaf that had pollen on it.” Others agree that the location of the experiment may have manipulated the results. Doyle Karr, corporate public relations manager for Pioneer, said that in a study conducted in 1998, a field that was planted with Bt corn showed a 40 percent increase in its monarch butterfly population. “This shows that field conditions are a big factor in determining mortality rates. The EPA [Environmental Protection Agency] has confirmed that this technology can kill butterflies, but what you have to look at is how often this will happen. In this case, the benefits of Bt corn protecting farmers fields outweigh the costs,” he said. While Obrycki acknowledges his experiment was conducted under lab conditions, he pointed out that the conditions were similar to field conditions. “I agree that this study for the most part was a lab experiment,” he said. “Although, the milkweed plants in our study were put out to capture actual field conditions. Also, the larvae in the lab could have chosen the other side of the plant leaf with no pollen on it.” Both Obrycki and Pioneer agree that more Bt corn research needs to be done. “Pioneer has worked in the past with the EPA and other agencies to study Bt corn and these efforts will continue in the future,” Karr said. Pioneer and Obrycki also agree that there is no research that shows that Bt corn can be harmful to humans. This is significant because Pioneer has 28 million acres of Bt corn planted across the nation, Karr said.