A new scientific study confirms a previous finding that pollen from genetically modified (GM) corn can kill monarch butterfly caterpillars, reigniting a heated debate over whether GM crops should be more strictly regulated. Researchers from Iowa State University found that more than half of monarch caterpillars studied died after being exposed for 48 hours to pollen from corn that had been engineered to produce the insecticide Bt. “In the field you may have higher mortality rates because of the cumulative effect of being exposed to the toxic corn pollen throughout the larval stage,” said scientist John Obrycki, coauthor of the study, which was published in the journal Oecologia. A separate study published last year found that monarch caterpillars could be killed by Bt corn pollen in a laboratory setting; this new study attempted to better replicate field conditions.