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A 37-year survey of monarch butterfly populations in north-central Florida shows that caterpillars and butterflies have been declining since 1985 and have declined by 80% since 2005.
Jaret Daniels, co-author of the study, program director and associate curator at the McGuire Center for Lepidopteran and Biodiversity Control at the Florida Museum of Natural History, reported a decrease along with a decrease in number of monarchs living in their wintering areas in Mexico.
"It's alarming in so many ways," said Daniels, an associate professor in the department of entomology and nematology at the University of Florida. "This study shows the close connection that exists between the monarch and the asclepi and highlights very dramatic abundance losses in Florida, which further confirm the decline of the monarch."
The researchers explained that decreasing native milkweed populations and increasing glyphosate use in the Midwest were part of the problem.
Glyphosate, a herbicide often applied in agricultural fields to control weeds, is deadly for milkweed, the host plant for monarch butterflies. Less milkweed means less habitat for monarchs, said Ernest Williams, co-author of the study, professor emeritus of biology at Hamilton College in New York.
"According to a general trend, 95% of corn and soybean products grown in the United States are glyphosate-resistant Roundup Ready crops," Williams said. "This has a national impact, what is really needed are areas of native vegetation and pesticide-free sources of nectar, not just for monarchs, but for all pollinators."
During the longest monarch-based location-based surveillance operation to date, a multi-institute team led by famed monarch expert Lincoln Brower, who died earlier this year, closely followed the number of spring monarch butterflies in a cattle pasture with no herbicides at Cross Creek, about 32 km southeast of Gainesville. The team examined milkweed plants in search of caterpillars and captured adult butterflies for 37 years, a period spanning more than 140 generations of monarchs.
They found that the spring departure of Mexico's monarchs coincided with the optimal growth of milkweed in the southeastern United States. Even though adult monarch butterflies can feed on a variety of plants, their young depend on milkweed as their sole source of food. toxins to ward off predators.
Monarchs lay hundreds of eggs on milkweed during their short lives, but just over 2% of the eggs survive to become fully developed caterpillars.
If monarchs arrive too early on their breeding grounds, they risk killing their host plants by frost – too late and these plants may not be able to feed their young. To maximize the chances of survival of their offspring, butterflies must plan to arrive in the United States within three weeks, said Daniels, which is an impressive feat for insects with a life span of six to eight years. weeks.
This delicate confrontation could be disrupted by climate change, which could skew the plant's spring calendars.
"Given that the timing is so tight, it would be devastating for the monarch," he said.
Florida is an important stopover for monarchs returning from Mexico from the north, while spring breeding in the southern states leads to recolonization by butterflies from the upper United States and Canada. Monarchs rely on Florida for its abundance of milkweeds and warm weather to lay eggs that will help replenish the eastern US population, Daniels said.
"Florida is kind of a gathering place for the recolonization of much of the east coast," he said. "If these populations are small, northern populations will have a similar level of abundance."
But although monarchs are a well-studied species, consistent long-term studies of changes in their spring breeding are rare, Williams said.
"Long-term studies like this are important because they indicate broader trends," he said. "Before 2005, the data fluctuated more and since 2005 the rate of decline has been stable."
Daniels said that increasing the population of pesticide-free native milkweeds in Florida shipyards and along the roads is a step in the right direction to prevent monarchs from seeking protection under the Endangered Species Act.
But, he said, no milkweed will do the trick.
Asclepias curassavica, or tropical milkweed, is a non – native tropical species marketed that has become popular with growers because of its color and vegetation all year round. However, tropical milkweed can become an "ecological trap" for monarchs, causing them to breed in unusual areas during the winter months – areas sufficiently distant from northern Mexico to remain freeze during and early of spring, Daniels said.
Prolonged reproduction may also lead to an increase in the protozoan parasite that infects Monarchs.
"It's not an absolute rule not to use this plant, but we want to be cautious about the potential implications," Daniels said. "It's always best to use aboriginal people in all areas."
Florida is home to about 21 species of native milkweeds. Daniels recommends either Asclepias incarnata, also called swamp milkweed, or Asclepias tuberosa, better known as butterfly moth. Asclepias humistrata, or milkweed, is also widespread in northern Florida and is essential for the recolonization of the monarch.
"It's not as simple as saying," We are planting milkweed and the monarch will be saved, "he said. "We should consider this an ecological problem, any organism or system is complex."
Daniels said the team would continue to monitor monarch butterfly populations in Florida. He stressed the Cross Creek owners' willingness to give the research team access to pastures every spring for 37 years, as a key factor in the study's success.
"This shows the importance of public-private relations in research," he said. "They were fantastic collaborators."
The main author of the study, Brower, died shortly before its publication. A long-time expert in the field of butterflies, Brower has been instrumental in the discovery of winter monarch colonies in Mexico, the researchers said. This is his final publication.
"He was really the big old man of the monarchs," said Williams. "No one has done more for the monarchs."
Williams said Brower had the gift of bringing people together and had worked with more than 160 people throughout his career.
According to his obituary in the New York Times, Brower began studying monarchs in the 1950s and made his first trip to the fir forests of Mexico, where butterflies spend the winter in 1977. In the 1980s Brower has worked with the Mexican government to protect forests from deforestation.
"The best thing to do is to continue his mission, study and work to conserve the monarch," Daniels said. "I think he'd be proud of this mission."
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