Other factors also contribute to population declines of the important pollinator.
By Kay Shipman, FarmWeek
The nutrition needs of a monarch butterfly are different from those of a caterpillar. Monarchs lay their eggs exclusively on milkweed plants that serve as a larvae food source. (Photo courtesy of USDA)
Monarch butterflies need milkweeds, but other plants also play important roles in the insects’ complex life cycle, said an Illinois Natural History Survey (INHS) scientist.
Plant ecologist Greg Spyreas, along with fellow INHS plant ecologist David Zaya, studies vegetation changes and potential impacts.
While decreased milkweeds, especially those in farm fields, contributed to monarch losses, “I don’t think that is the complete picture,” Spyreas told FarmWeek.
Illinois is developing two monarch strategies. One will become part of a multistate monarch flyway plan, which will be submitted to U.S. Fish and Wildlife; the other will be an Illinois plan to guide conservation efforts and be in place should monarchs become a threatened or endangered species.
Milkweeds remain critical in the monarch life cycle. The monarchs arrive in Illinois in May and June when milkweed emerges, Spyreas noted. Monarchs lay their eggs exclusively on milkweed plants that serve as a larvae food source.
“To produce one adult, you need one milkweed plant,” Spyreas said.
However, the plant ecologist draws a distinction between caterpillar needs and adult butterfly needs. Adult needs for nectar sources are different, he added. Migrating monarch butterflies “move great distances along the landscape” and take nectar from wildflowers along their route, Spyreas said.
Initially, milkweed decreases and monarch declines occurred about the time farmers adopted herbicide-resistant crops and fields became more weed-free, Spyreas said. However, despite milkweed decreases in farm fields, monarchs are using wild habitat milkweeds in natural areas and along roadsides and rights of way, he added. The natural areas are buffering milkweed losses from farm fields and allowing monarchs to build their populations during the summer.
Efforts to promote planting milkweeds in backyards, parks and other small plots provide another boost, according to Spyreas. “We can do a lot of good having a few milkweeds,” he said.
Taking a big-picture view of the monarch life cycle leads Spyreas to suggest other factors contribute to monarch decreases.
“When you look at the regional trend decline in the Midwest of adult monarch numbers, we have not seen the decline in numbers like in Mexico,” he said. “Something is happening in the fall migration to Mexico that causes the losses.”
The public attention being given to monarchs is warranted, according to Spyreas, who added “we’re talking what was the most common butterfly in the U.S.”
As for government monarch strategies, “we do not know what the smoking gun is for the decline. … We have a lot of environmental problems,” Spyreas said. “It is not necessarily one thing, but a lot of things that add up.”
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