In 2015 research very clearly showed that monarchs breeding on tropical milkweed (Asclepias currasavica) throughout the winter have higher levels of protozoan infection caused by Ophryocystis elektroscirrha, compared to monarchs in the migratory cycle.
When Tropical Milkweed is planted in the coastal U.S., these plants continue to flower throughout the fall and winter if there are no freeze events. And due to climate changes, the Monarchs are not finishing their fall migration. This is adverse effects Monarch breeding during this time.
Monarchs are staying longer in areas where they would not normally stay over winter; therefore, subjecting them to devastating freezes.
Because Monarch butterflies are staying longer in the United States, they are exposed to a deadly protozoan parasite known as Ophryocystis elktroscirrha (OE).
The deadly disease spores of OE build up on overused Tropical milkweed plants. Continuous breeding on the same plants can lead to the OE infection being spread to Monarchs too. This is then being passed from infected butterflies to healthy ones.
Recent research studies show prolonged exposure to parasites, increased risk of infection, and the spread of more virulent parasite genotypes in Monarchs. This is a huge problem mainly in U.S. coastal regions including Florida, Texas, and Southern California.
What Can We Do About It?
- Plant native milkweeds whenever possible and gradually replace your tropical milkweed with native species.
- If you have tropical milkweed, cut it back from October-February to within 6″ of the ground. Also, remove any new plant growth at the base of the plant; it will be necessary to prune frequently (every 3 weeks) as it re-grows.
Though there are twenty native species of milkweed in Florida, only three varieties are generally available in nurseries: Butterfly Milkweed (Asclepias tuberosa), Swamp Milkweed (Asclepias incarnate) and Aquatic Milkweed (Asclepias perennis).
By planting the correct type of species of native milkweed, you can help maintain a safe and natural food source for monarchs, creating healthier populations.
Overuse is not a problem with native milkweeds because the leaves are only desirable to Monarchs during the early part of the growth cycle, unlike that of non-native Tropical Milkweed that remains desirable from the first leaf to the first frost. Native milkweed species will not disrupt the migratory patterns of Monarchs during fall.
You can make your landscape friendly for Monarchs throughout their lifecycle by creating a safe environment for them to lay eggs, sip nectar, or find shelter on nippy evenings. Plant more native milkweeds such as Swamp Milkweed for Monarchs to lay eggs on and also for caterpillars to eat.
Since Monarchs are insects, spraying insecticides will kill them. So, avoid spraying pesticides in your yard. Encourage natural controls such as birds and beneficial insects, with the use of native plants for food sources, nesting opportunities, and shelter, for maintaining balance in your landscape.’
Unfortunately, this is not the only problem the Monarch faces. Some other issues are…
- Tachinid Flies
- NPV (Nuclear Polyhedrosis Virus)
- Pseudomonas (Bacterial Disease)
- Trichogramma Wasps
- Chalcid Wasps
- Anal Prolapse
- Bacillus thuringiensis (BT)
In the longest location-based monarch monitoring effort to date, a multi-institute team led by world-renowned monarch expert Lincoln Brower, who passed away in 2018.
The group closely followed spring monarch numbers in an herbicide-free cattle pasture in Cross Creek, about 20 miles southeast of Gainesville. Furthermore, they examined milkweed plants for caterpillars and captured adult butterflies for 37 years, a period spanning more than 140 generations of monarchs.
Study co-author Ernest Williams, professor emeritus of biology at Hamilton College in New York. confirms that Monarchs lay hundreds of eggs on milkweed over their brief lifetimes, but just over 2 percent of eggs survive to become fully grown caterpillars.
“Florida is kind of a staging ground for the recolonization of much of the East Coast,” Williams said. “If these populations are low, then the northern populations are going to be at a similar abundance level.”
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 point to larger trends,” he said. “Before 2005, there was more fluctuation in the data. Since 2005, the rate of decline has been steady.”
Daniels said that increasing pesticide-free native milkweed populations in Florida yards and on roadsides is a step in the right direction to prevent monarchs from requiring protection under the Endangered Species Act.
The study co-author Jaret Daniels, program director and associate curator of the Florida Museum of Natural History’s McGuire Center for Lepidoptera and Biodiversity, said the team will continue monitoring monarch populations in Florida. He highlighted the willingness of Cross Creek property owners to give the research team access to the pastures each spring for 37 years as a key factor in the study’s success.
“It shows the importance of the public and private relationship when it comes to research,” he said. “They’ve been fantastic collaborators.”
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