A 37-year survey of monarchy populations in North Central Florida shows that caterpillars and butterflies have declined since 1985 and have fallen by 80% since 2005.
This reduction is in line with the weakening of monarchy numbers in areas living in Mexico, as co-author of the study, Jaret Daniels, program manager and associate editor of the McGuire Center for Florida, Lepidoptera and Biodiversity.
"It's worrying in a number of ways," said Daniels, who is also an associate professor in the Department of Intrinsic and Neutrology at the University of Florida. "This study shows the close relationship between a monarch and a dairy producer and stresses very dramatic losses in abundance in Florida that further confirm that the monarch is decreasing."
Although the drivers of decline are not clear, the researchers said that shrinking indigenous dairy live populations and a boost to the use of glyphosate in the Mediterranean are part of the problem.
Glyphosate, a herbicide often applied in agricultural fields to eradicate weeds, is deadly for dairy, the host plant of the monarchs. Less dairy means less of a habitat for monarchs, said co-author of the study, Ernest Williams, biology professor at Hamilton College in New York.
"A broad standard is that 95 percent of corn and soy products grown in the US are Roundup Ready crops that resist glyphosate," said Williams. "This has a national impact. What really needs is the patches of natural vegetation and nectar sources, without pesticides, not only for monarchs but for all pollinators.
In the biggest monarch tracking effort based on the location so far, a multinational team headed by world renowned monarch expert Lincoln Brower, who died earlier this year, closely watched monarch numbers on a no-botanical pasture at Cross Creek, 20 miles southeast of Gainesville. The team examined dairy plants for caterpillars and captured butterflies for 37 years, a period of more than 140 generations of monarchs.
They found that the departure of the spring of the monarchs from Mexico is dated to coincide with the optimum development of dairy dough in the southeastern US. While monarchal adult butterflies can be fed by a variety of plants, their young people are dependent on dairy production as the only food source, toxins to ward off predators.
The monarchs put hundreds of dairy eggs over their short life, but over 2% of the eggs survive to become fully-growing caterpillars.
If the monks reach the breeding sites very early, they run the risk of their host plants being killed by the frosts – too late and the plants may not be able to support their young. To maximize the survival chances of their offspring, butterflies must date their arrival in the US within a three-week window, Daniels said, an impressive call for insects with a shelf life of six to eight weeks.
This fine match could be disturbed by climate change, which can ridicule plant spring programs.
"As it is so narrow, it would be devastating to the monarch," he said.
Florida is an important stop for monarchs returning north from Mexico, as springtime reproduction in the southern states leads to the revival of the butterflies of the upper US and Canada. Monarchs rely on Florida for the abundance of milk and warm climate to lay eggs that will help rebuild the eastern population in the United States, said Daniel.
"Florida is a kind of space for the reclassification of much of the East Coast," he said, "If these populations are low, then the northern populations will be at a similar level of abundance."
But although the monks are a well-studied species, continuous long-term studies of changes in their reproduction are rare, said Williams.
"Long-term studies like this are important because they show the biggest trends," he said. "Before 2005, there were more fluctuations in the data. Since 2005, the rate of decline has been steady."
Daniel said the increase in indigenous non-pesticide dairy farmers' populations in Florida yards and road arteries is a step in the right direction to prevent protection from monarchs under the Law on Endangered Species.
But, she said, she would not make any milk.
Asclepias curassavica or the tropical dairy is a commercial, non-indigenous tropical species that has become popular with growers due to its color and vegetation. But tropical dairy farmers can become an "ecological trap" for monarchs and force them to breed in unusual areas in the winter months – areas quite north of Mexico to remain prone to freezing events throughout the winter and early spring.
Prolonged reproduction may also lead to an increase in protozoa that infects monarchs.
"It's not a tough and fast rule of non-use of the plant, but we want to be careful about possible impacts," said Daniels. "It's always better to use natives all over the ship."
Florida hosts about 21 native milk. Daniels recommends either Asclepias incarnata, also called Swamp milkweed, or Asclepias tuberosa, commonly known as butterflyweed. Asclepias humistrata, or pine tree pine, is also common throughout North Florida and is indispensable for the reign of the monarch.
"It's not as simple as we say," we plant dairy and the monarch will be saved, "he said." We have to think of it as an ecological issue. There is great complexity in every organization and system. "
Daniel said the team will continue to monitor the monarch population in Florida. He stressed the willingness of Cross Creek owners to give the research team access to pastures every spring for 37 years as a key factor in the success of the study.
"It shows the importance of public and private research relations," he said. "They have imagined collaborators."
The chief author of the study, Brower, died shortly before publishing. A life-long butterfly expert, Brower has made a decisive contribution to finding monarchic colonies in Mexico, according to researchers. This is the final publication.
"He was really the great old monarch," Williams said. "Nobody has done more for monarchs."
Williams said Brower had the ability to bring people together and worked with more than 160 partners throughout his career.
According to his graveyard at The New York Times, Brower began studying monarchs in the 1950s and made his first trip to the Mexican firs, where the butterflies go through the winter in 1977. In the 1980s, Brower collaborated with the Mexican government to protect forests from deforestation.
"The best we can do is to continue his mission and continue studying and working to preserve the monarch," said Daniel. "I think he will be proud of this mission."