Apparently so, from personal observation.
Over the years, we've grown multiple species of milkweed in our pollinator garden in Vacaville, Calif. We give them a choice. The species include:
- Narrow-leafed milkweed, Asclepias fascicularis
- Showy milkweed, A. speciosa
- Pleurisy root, A. tuberosa
- Tropical milkweed, A. curassavica
- Hairy balls or balloonplant, Gomphocarpus physocarpus
Which species do they prefer? Tropical milkweed, hands down. But it's a plant that's become highly controversial in California. Friends unfriend friends, and the unfriended lash out with how "bad" tropical milkweed is and how "uneducated" the messenger is. "Don't you know about Ophryocystis elektroscirrha (OE)?" they ask. "How dare you plant tropical milkweed? Yank it out!"
Meanwhile, the monarchs keep monarching. And we keep observing them.
Consider the male monarch spotted lying in the middle of a residential street in west Vacaville the morning of Jan. 3. It was there despite the rain, the cold and the passing cars. What will happen to it? Will it find a mate? Will its mate be able to find a milkweed to deposit her eggs? She certainly won't find native milkweed, such as A. fascicularis and A. speciosa, but she might find A. curassavica.
If. She. Is. Lucky.
Mona Miller, administrator of the educational Facebook page, Creating Habitat for Butterflies, Moths and Pollinators, recently shared a post that should be "food for thought" (for us) and that should result in "more food" (milkweed) for the monarchs. Her Facebook page focuses on "the preservation and protection of North American butterflies, moths and pollinators, particularly the Monarch butterfly."
"All milkweeds get Ophryocystis elektroscirrha (OE)," Miller wrote. "There are native milkweeds that are viable in the fall and winter. Tropical milkweed, due to their high level of toxins (cardenolides), are very medicinal. Monarch females choose tropical milkweeds over less toxic native plants to self-medicate. In October 2022, there was a discussion on the Monarch Watch email list. Dr. (Orley "Chip") Taylor (founder and director of Monarch Watch and a professor in the Department of Ecology and Evolutionary Biology at the University of Kansas) said that tropical milkweed does not stop the migration. He said more native and tropical milkweed should be planted. He said the more milkweed that is available the less spores will be left on all milkweeds. Fewer milkweeds leave monarchs visiting available milkweeds and leaving more spores. You can read the discussion here, there are several posts: https://lists.ku.edu/pip.../dplex-l/2022-October/012192.html."
"Actually, the best strategy is to plant more milkweeds, both native and tropical," Professor Taylor wrote, explaining that "First, the interactions between monarchs, milkweed and O.E. are frequency and density dependent. What this means is that spore loads on foliage are dependent on the abundance of milkweed relative to the number of ovipositing females. The O.E. infection rate is a function of this dynamic. Second, because of these relationships, O.E. cycles. That is, it increases and then declines only to increase again. There is a seasonal pattern to these cycles with low rates in the spring and higher rates about 3-4 generations. Third, the interactions that contribute to cycling involve spatial relationships that include distances between resources (milkweed patches) and the search capabilities of the butterflies. There is a time component as well."
"Here is the scenario that could play out from San Diego to Ventura counties and parts of Marin as well," Taylor wrote. "Due to warmer conditions more and more native milkweeds (mostly fascicularis) remain green during the winter. This appears to be happening over a broad area. With the sale of tropical milkweed (hereafter TM) being prohibited and homeowners being discouraged from growing TM, what is the likely outcome? With fewer milkweeds overall, the O.E. spore count will go up on both native and TM. OE will become more common rather than less. Further, the reduced distribution of milkweeds will reduce the opportunity for O.E. to cycle. Cycling depends on part of the milkweed distribution being relatively free of spores for the monarch population to recover. Overall, there will be fewer butterflies surviving the winter and therefore a lower starting population in the spring. If that happens, there will be fewer monarchs through the entire season. So, instead of leading to lower O.E. and more butterflies, the elimination of TM is likely to reduce the monarch population--in effect taking the butterflies away from the people. Again, in addition to cutting back TM from time to time to reduce O.E., an alternative solution is to grow TM and to see that it is hyper-dispersed in gardens, etc. through the 5-county area. The same strategy would involve A. fascicularis and other native milkweeds."
"Some of the reaction to TM is simply based on the notion that it is non-native," Taylor wrote. "We can agree on that point. However, it does not naturalize and therefore is not invasive. Our gardens are filled with such plants. TM supports populations of monarchs as far south as Peru and in most, if not all, places where monarchs have been introduced. Also, since this species flowers nearly continuously through the growing season, it is a source of nectar for a large number of pollinating species. TM supports monarchs--full stop! Let's learn to live with it. More milkweeds equal more monarchs and less O.E. overall."
Taylor went on to say that TM does not cause monarchs to break diapause and become reproductive. "Dingle suggests that it is temperature that causes monarchs to break diapause and that is exactly what I have been saying for years. Hormone production is a function of temperature--head temperatures--and not contact with plants. The major driver in the West has been and will continue to be weather/climate. It starts with the conditions that determine the size and distribution of the overwintering female numbers and their reproductive success."
However, the California Department of Food and Agriculture (CDFA), influenced by conservation groups, has categorized A. curassavica as "a noxious weed," and county agricultural commissioners have banned the sale of the plant in nurseries in Marin, Contra Costa, San Mateo and Ventura counties.
Professor Dingle bears to differ. "No one should rush out and pull out their tropical milkweed as it would be a waste of time and effort," he says. "Nurseries should also be able to continue to sell it." He points out:
- "There is not enough tropical milkweed planted to have much influence (see the amount of A. syriaca and A. fascicularis throughout the American west not to mention various other species like A. erosa, cordifolia, californica, etc.) Yes, there are parasites on A. curassavica as there are on ALL milkweeds."
- "There are populations of monarchs that are doing just fine feeding exclusively on A. curassavica (e.g. on many Pacific Islands, such as Guam where I have studied them.
- "Migration and the diapause that accompanies it in the fall are determined by shortening photoperiod and temperature (warm temps can override short days hence the issue with climate change). There is no significant influence of food plant."
UC Davis distinguished professor Art Shapiro, who has monitored butterfly populations in central California since 1972, says the "anti-curassavica propaganda is total hogwash. I have been saying so for years."
Curious, isn't it, that a plant can be so controversial? Four states, California, Arizona, New Mexico and Texas, border Mexico. On the California side, inches away from the Mexican border, tropical milkweed is considered a "noxious weed" per the CDFA definition. On the other side, in Mexico, it's simply a great host plant for monarchs.
What does 2023 hold for the iconic monarch and its host plants? For one thing, more scientific research is needed.
"Insect populations are well known for large annual fluctuations in size. However, rarely do these fluctuations occur on the scale currently being seen in western monarchs. From less than 2,000 monarchs counted in 2020, we currently have more than an estimated 200,000 at the overwintering sites! A 100-fold increase! This is staggering! However, it is less of a surprise to me than many others. In March 2021, I published a commentary paper titled Western North American Monarchs: Spiraling into Oblivion or Adapting to a Changing Environment? (Animal Migration journal). I suggested the latter was the case and stated: ‘the adaptability of the monarch butterfly will allow it to persist in a changed environment'. I based this on more than 40 years study of monarch populations, particularly research I did, published in peer-reviewed journals, that showed monarchs in Australia (they arrived in 1870 by island-hopping across the Pacific) had adapted physiologically to Australian conditions. I think we are seeing this monarch ‘power' now. They are trying different things in terms of life strategies and inevitably there will be failures and successes. This is how insects adapt and evolve. We will see more ups and downs in the future, but I have seen how adaptive and resilient the monarch is. This isn't to say we shouldn't help the monarch. We should and we are, primarily by creating habitat and reducing pesticide use. We can work with the adaptable and resilient monarch and ultimately turn 200,000 into 2,000,000!"
Mona Miller, who administers the popular Facebook page, Creating Habitat For Butterflies, Moths, & Pollinators, responded to the WSU post: "Monarch are resilient insects, they have so many strategies to increase their population, but they do have their limits. We must stop pulling out tropical milkweed and cutting it back. Washing off all milkweed should suffice to clean off the OE spores. I emailed several scientists, no one could tell me that OE (Ophryocystis elektroscirrha is a protozoan parasite) has any way to attach to milkweed leaves other than getting caught in the hairs. Tropical milkweed has smooth leaves. Tropical milkweed has been in California since 1909, that is over 100 years. Totally eradicating tropical milkweed just like totally eradicating all the eucalyptus trees would have a detrimental effect on the Monarch population, perhaps it already has." (Note: both eucalyptus trees and tropical milkweed are non-natives.)
"Do plant native milkweeds and nectar sources," she advocates. "If you don't have land, plant these plants in containers. Any habitat is critical to help feed the pollinators including Monarch butterflies."
In response to a post that "Tropical milkweed and eucalyptus trees are not native to Ca regardless of how long they have been here," Miller pointed out: "There are many plants growing in California that are not native to California. The fact is that the Monarch butterflies are using both of these plants. If these plants are immediately eradicated it would be compromising shelter, nectar, and host plants for the Monarch butterfly. During the winter both are blooming and provide nectar. Cutting back tropical milkweed when it has caterpillars in the winter should not be done. How is the Monarch butterfly going to evolve to adapt to the weather without tropical milkweed? Like I said, just wash off all milkweeds to clean off the OE. Due to changes in weather, there are also some native milkweeds that are not dying back in the winter. We can help the Monarch butterflies adapt or we can pull the rug out from under them by continuing to eradicate the plants that they need for winter survival."
Another point: Monarchs aren't native, either. Read Lincoln Brower's "Understanding and Misunderstanding the Migration of the Monarch Butterfly (Nymphalidae) in North America: 1857-1995" (Journal of the Lepidopterists' Society 49(4), 1995,304-385.) It begins: "Since 1857, amateurs and professionals have woven a rich tapestry of biological information about the monarch butterfly's migration in North America. Huge fall migrations were first noted in the midwestern states, and then eastward to the Atlantic coast. Plowing of the prairies together with clearing of the eastern forests promoted the growth of the milkweed, Asclepias syriaca, and probably extended the center of breeding from the prairie states into the Great Lakes region. Discovery of overwintering sites along the California coast in 1881 and the failure to find consistent overwintering areas in the east confused everyone for nearly a century. Where did the millions of monarchs migrating southward east of the Rocky Mountains spend the winter before their spring remigration back in to the eastern United States and southern Canada? Through most of the 20th century, the Gulf coast was assumed to be the wintering area, but recent studies rule this out because adults lack sufficient freezing resistance to survive the recurrent severe frosts."
Art Shapiro, UC Davis distinguished professor of evolution and ecology who maintains a research website at http://butterfly.ucdavis.edu/, weighed in on the issue today in an email about the monarch population increase: "We do not know where they are coming from. This merely goes to show (1) how spotty our coverage is. (2) how little we understand about life-history plasticity in this species. (3) that most of the received wisdom about the decline and its causes is bunk."
Shapiro has monitored butterfly population trends on a transect across central California since 1972. The 10 sites stretch from the Sacramento River Delta through the Sacramento Valley and Sierra Nevada mountains to the high desert of the Western Great Basin. The largest and oldest database in North America, it was recently cited by British conservation biologist Chris Thomas in a worldwide study of insect biomass.
We remember when Shapiro observed an way-early monarch in Sacramento on Jan. 29, 2020. Later in the afternoon, he heard monarch scientist Elizabeth Crone, professor of Tufts University, present a UC Davis Department of Entomology and Nematology seminar on the decline of Western monarchs.
In her seminar, Crone expressed concern about the lack of scientific knowledge about monarchs, especially when they emerge from their overwintering sites along coastal California, usually around February, and head inland. Said Crone: "We don't know what they're doing between February and when milkweeds break ground later in spring."
There is so much we do not know about monarchs...
UC Davis-affiliated resource, published Nov. 17, 2020 in Proceedings of the National Academy of Sciences (PNAS):
"Two Centuries of Monarch Butterfly Collections Reveal Contrasting Effects of Range Expansion and Migration Loss"
We walked into our little pollinator garden in Vacaville, Calif., this afternoon to cut a few tropical milkweed stems to feed the indoor caterpillars, and there, hidden beneath a leaf, was a tiny caterpillar.
Well, hello, there! Aren't you a little late? The monarchs have been overwintering along coastal California for a couple of months. Your parents did not get the memo.
This uncharacteristic weather we're having--autumn temperatures soaring into the 70s here in recent weeks--means the milkweed is still growing and the caterpillars are, too.
We've pruned all of the tropical milkweed down to the ground except for one plant that's still flowering. We're keeping it. Food is scarce for the honey bees, syrphid flies and other pollinators.
Meanwhile, Tiny Caterpillar is a new addition to our indoor habitat. Ours is just a small-scale conservation project of rearing and releasing monarchs to help boost the declining monarch population. So far this season, our total is 54. That's 54 that may have been eaten by birds or consumed inside-and-out by parasitoids such as the tachinid flies, which lay their eggs inside the caterpillars or chrysalids. Overall, about 2 or 3 percent of the monarchs make it all the way through their life cycle, from egg to caterpillar to chrysalis to adult, scientists estimate.
Here are the basics of how we rear them, but all Monarch Moms and Monarch Dads do it differently.
- Grow milkweed species, the host plant of the monarchs. We have four different species in our pollinator garden:
--Asclepias fascicularis, narrowleafed milkweed
--Asclepias speciosa, broadleaf milkweed
--Asclepias tuberosa, a Midwest favorite
--Asclepias curassavica, tropical milkweed
- In addition to milkweed, plant other nectar-producing plants for your monarchs and other pollinators. The monarch favorites, at least in our yard, include Mexican sunflower (Tithonia), an annual that grows here from April through November (in fact it's still blooming), butterfly bush (Buddleia), and Lantana.
- When you see caterpillars on the milkweed, you'll need to protect them from predators, such as birds, tachinid flies and wasps by bringing them indoors. Add water to a heavy, narrow-necked, flat-bottomed bottle (we use Patron tequila bottles, compliments of our friends). Tuck the milkweed stems, with the 'cats still on the stems, in the tequila bottle. Then place the bottle in a meshed, zippered butterfly habitat, such as the ones from the Bohart Museum of Entomology. You can also buy meshed, zippered laundry bags from stores.
- Be sure to keep the milkweed fresh. Mist it lightly, and add new milkweed daily. Clean the frass from the bottom of the habitat.
- Watch caterpillars eat their fill and then pupate. You'll see the jade-green chrysalids, rimmed in gold, hanging from the top of the habitat.
- When the monarchs eclose, wait for their wings to dry before releasing them. We usually release them after four or five hours--if it's not cold or rainy. Food? They usually won't eat for 24 hours. If the weather is inclement and we can't release them right away, we feed them. We dip a cotton ball into a mixture of honey and water, and place it on a tray, along with a fresh flower or a slice of fruit, such as cantaloupe or watermelon. Some folks feed them a sugar and water mixture. Some use sports drinks such as Gatorade. Mona Miller, administrator of the Facebook page, Raising Butterflies and Moths for Conservation, tells how to feed monarchs on her YouTube channel. She uses 2 tablespoons of water (heated) and 1/2 teaspoon of raw organic honey (more amino acids and protein). She cools the mixture and places in a colorful cap lid (yellow, red, orange).
- When it's time to release a monarch, we just unzip the container. Sometimes we gently cradle the monarch, and then open our hands and watch it go. Some monarchs take off immediately. Others linger on our hands or head for a nearby plant.
- After you release each batch of monarchs, clean the container with soapy water and a little bleach.
Some excellent resources to get you started and keep you going:
- Xerces Society: Monarchs for Conservation and Project Milkweed
- The Beautiful Monarch, Facebook page administered by Holli Webb Hearn
- Raising Butterflies and Moths for Conservation, Facebook page administered by Mona Miller