Two researchers at Cornell say the factors behind the decline in monarch butterfly populations are wider spread than the loss of milkweed, their summertime food source. They say the list includes sparse nectar sources in the fall, adverse weather and fragmentation of habitat.
Cornell professor Anurag Agrawal, the senior author of the paper, says with more information about the life cycle of the iconic orange-and-black insect, the research team was able to make inferences about the challenges facing the monarch. “The group found problems in the transition from the U.S. and southern Canada to the overwintering grounds in Mexico,” says a Cornell release. “The problem appears to occur after they take flight in the fall.” The researchers “did not find evidence supporting the ‘milkweed-limitation hypothesis.'”
The American Soybean Association pointed to the Cornell research in a statement that called on farmers to help preserve the butterfly. “Be aware of existing milkweed in your non-crop areas,” said an ASA official. “Please don’t spray. These milkweed are critical for the survival of this species. While this new study suggests Monarchs are facing several challenges, we can do our part to ensure a sustainable population.” Some environmentalists say the 90-percent decline in monarch numbers over the past two decades is tied to larger corn and soybean plantings and use of herbicides against weeds on cropland.