- Author: Kathy Keatley Garvey
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.
- Author: Kathy Keatley Garvey
Fact: Without milkweed, no monarchs.
Yet a milkweed species that's been thriving in California for more than a century is getting a bad rap. The California Department of Food and Agriculture (CDFA), apparently influenced by conservation groups, has categorized Asclepias curassavica, commonly known as tropical milkweed, as "a noxious weed."
That means, among other things, that county agricultural commissioners can ban the sale of tropical milkweed in nurseries. Indeed, several counties, including Marin, Contra Costa, San Mateo and Ventura, already have.
Banned for sale in nurseries? Says entomologist Jeff Smith, who curates the Lepidoptera collection at the Bohart Museum of Entomology: "There are PLENTY of other 'noxious' weeds sold in nurseries (eucalyptus?) that don't seem to raise the hackles of these counties, so it appears more political than factual, and coming up with the supposed pathogens-on-the-plants scenario looks like they searched for an excuse."
Fact: Infected monarch butterflies can deposit microscopic protozoan parasites, Ophryocystis elektroscirrha or OE, on milkweed. That's ALL species of milkweed, not just tropical. Tropical, however, does not die back in the winter in some parts of California, and that, some argue, encourages monarchs to continue to breed and impedes their migration to overwintering sites. Some blame this "continued OE exposure" to the decline of the monarch population.
Hugh Dingle, distinguished professor emeritus of entomology, behavior and evolution at UC Davis and now a Marin County resident, is an internationally known expert on animal migration. He's researched animal migration for some 50 years. In the last 20 years or so, he has focused on monarch butterflies. He has authored two editions of Migration: The Biology of Life on the Move and some 100 papers. National Geographic featured Professor Dingle in its cover story on “Great Migrations” in November 2010. LiveScience interviewed him for its November 2010 piece on “Why Do Animals Migrate?” (See news story that includes his biographical information)
Professor Dingle responded to a recent front-page article in a Marin County paper about the ban on tropical milkweed. Banning tropical milkweed will NOT save the monarch, Dingle told the reporter in an email. In fact, he said, the ban will "essentially have zero effect on monarchs" and "no one should rush out and pull out their tropical milkweed as it would be a waste of time and effort. Nurseries should also be able to continue to sell it."
The contents of his email, which the professor shared with Bug Squad, include:
- "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."
They Should Know Better! Dingle said some of the advice that CDFA received to categorize A. curassavica as a "noxious weed" came from conservation groups. "They should know better!" he declared.
Art Shapiro, UC Davis distinguished professor of evolution and ecology, has been researching the butterfly populations (including monarchs) of central California for more than 50 years. He co-authored the well-cited research article, "Understanding a Migratory Species in a Changing World: Climatic Effects and Demographic Declines in the Western Monarch Revealed by Four Decades of Intensive Monitoring," published online in March of 2016 in the journal, Population Ecology.
Professor Shapiro shared this email with Bug Squad:
So, What Happened? We asked Professor Dingle how tropical milkweed went from total acceptance to a bad reputation. "I don't know why tropical milkweed got such a bad reputation," he responded in an email. "A couple of possibilities: in some places tropical milkweed seems to have more of the Oe parasite than temperate species which die back in winter--ergo, butterflies pick up more parasites (Fact is not enough to have much influence on migration or breeding although in some places there can be a little. But over the whole range of monarchs . . .naaah!) Second possibility is since tropical is around longer, butterflies can feed on it longer and so might 'keep butterflies from migrating.' BUT...migration is a photoperiodic phenomenon (occurs with short days) so feeding is irrelevant. Besides during migration monarchs will feed on almost any plant with nectaring flowers!"
"Monarch butterflies are dependent upon milkweed as its host plant. They lay their eggs on milkweed and their caterpillars eat milkweed. In the past, monarchs in California spent the winter roosting in trees along the coast of California. They did not breed during the winter. They moved inland during summer months where they bred."
"Because of global warming, monarchs have begun to breed during the winter months in California and the existence of tropical milkweed in gardens in coastal California has made that possible...The Nature Police have succeeded in getting the sale of tropical milkweed banned in Contra Costa, Marin, San Mateo and Ventura counties. Academic entomologists have pushed back against this harmful ban in an article published by The Monterey Herald, San Jose Mercury, Marin Independent Journal, and East Bay Times.
The milliontrees.me website also points out that:
- Hugh Dingle, a retired University of California at Davis entomology professor who has studied monarch butterfly migration for more than two decades, said the bans are “basically a wasted effort” and that the focus should be on larger threats such as pesticide and herbicide use. All species of milkweed carry parasites that can affect monarch populations."
- “Arthur Shapiro, a UC Davis professor who has studied monarch butterflies for the past six decades, described the rationale behind the bans as “hogwash.” Shapiro, Dingle and other researchers said winter breeding among monarch butterflies is a relatively new behavior and one influenced by warmer winter temperatures caused by climate change.”
- “David James, an associate entomology professor at Washington State University who has studied monarch butterfly breeding and migration in the Bay Area, said there is a case to be made about the tropical milkweed as being a vital resource for the monarchs in a changing climate.”
- “Leslie McGinnis, a UC Berkeley doctoral candidate studying monarch populations and working with gardeners in the East Bay, said the bans take a 'simplistic view' of the threats that monarchs face, including the fact that many native milkweed plants supplied to nurseries can also be sprayed with pesticides. The bans, she said, can work to disenfranchise or demonize people that have tropical milkweed who instead could be partners in working to help restore monarch populations.”
Indeed, the website minces no words: "Native plant advocates are wedded to a past that is long gone. The climate has changed and it will continue to change. Monarchs and other animals are trying to adapt to the changed conditions. Their survival depends on their ability to adapt. The native plant movement has become a form of climate change denial. Their irrational hatred of introduced plants is damaging the environment with herbicides and harming wildlife. There is no evidence that tropical milkweed is harmful to monarchs."
Mona Miller, who administers the popular Facebook page, Creating Habitat For Butterflies, Moths, & Pollinators, related in a recent 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." (Both eucalyptus and tropical milkweed are non-natives.)
Personal Experience. As an aside, our family has provided several species of milkweed in our pollinator garden in Vacaville for more than a decade. The species now include narrowleaf milkweed, A. fascicularis; butterflyweed, A. tuberosa; showy milkweed, A. speciosa; and tropical, A. curassavica. One season we counted more than 300 eggs and caterpillars on the milkweed. Almost all favored A. curassavica. Second choice: A. fascicularis. Some scientists say that perhaps tropical milkweed offers more toxins, and monarchs "know what they want and need."
We continue to plant both natives and non-natives in our thriving garden. The practice now seems so highly controversial that sometimes we feel as if we must mark ourselves "safe" from negativity. But as Professor Shapiro told Bay Nature in June 2022: "I am sick to death of being told you must use natives, especially if a butterfly has no more interest in it than a fire hydrant."
Additional Resources:
- Milliontrees.me:
The Consequences of Putting Plants into 'Native' Strait-Jackets - "Monarch Butterfly Experts Fault Marin Tropical Milkweed Ban," published in, among others:
Ukiah Daily Journal
Marin Independent Journal
Chronicles Live - Xerces Society of Invertebrate Conservation
Monarchs in Decline
Native Milkweeds - Bug Squad:
What's Happening with Our Western Monarch?
- Author: Kathy Keatley Garvey
And how long misinformation can linger...
Take the news about the overwintering 250,000 monarchs recorded along the California coast in the Western Monarch Thanksgiving Count spearheaded by the Xerces Society for Invertebrate Conservation. That's more than a 100-fold increase from the previous year.
Butterfly guru Art Shapiro, a UC Davis distinguished professor of evolution and ecology who has been monitoring butterfly populations in Central California since 1972--and maintains a research website at https://butterfly.ucdavis.edu--wants to know where they came from. He acknowledges he does not know, nor does anyone else. Yet.
Lynn Kimsey, director of the Bohart Museum of Entomology and a UC Davis distinguished professor of entomology, says we shouldn't consider the population increase a trend, that it's still too early to figure out what's going on.
Says Bohart associate Greg Kareofelas: "I think it is hopeful, but we will not know for sure until 5 or 10 years have gone by. One year is not a trend."
- "It is great to have more breathing room, but we're not out of the woods yet, in terms of conservation. The current population is still < 5% of our estimates from the 1980's and has only been that large for one year."
- "When populations reach unprecedented sets of conditions (in this case, lower overwintering numbers than we had ever seen before, from 2018-2020), we should expect the unexpected. And one thing to emphasize is"
- "We expect large fluctuations in abundance of butterflies and many other insect species. We need to manage for resilience, because we probably won't be able to understand every crash or rebound." (See her UC Davis seminar)
But a key point is this: "There are NOT two populations of the monarch in North America," says migration expert and monarch scientist Hugh Dingle, emeritus professor, UC Davis Department of Entomology and Nematology. "The population is all one and the butterflies from all over North America mix in Mexico during the winter diapause. The monarchs breeding in the west (of the Rockies) have at least two (and probably three) migration routes in the fall--one is to the California coast, one is down the Colorado River Valley into Mexico, and the probable third is east of the Great Salt Lake and west of the Wasatch down through eastern Arizona and into Mexico. Sample sizes are small for the third route which is why it is only probable. Also genetic data going back 50 years shows that the North American population is all one, that is, work by Walter Eanes and others including recent molecular genetics studies!"
The western migration routes are outlined in Dingle et al. Biological Journal of the Linnaean Society 85:491-500 (2005), and for various evolutionary changes in monarch migration and correlated characters see Freedman, Dingle, et al. B. J. Linn. Soc. 123:265-278 (2018), Animal Migration 5:61-73 (2018), and the Proceedings of the National Academy of Sciences (PNAS) 117: 28887-28893(2020) and references therein.
Commented Dingle: "The old saw about two North American populations is a good example of once something gets into the literature--or into the public domain-- it becomes exceedingly difficult to correct."
Now scientists are trying to figure out what contributed to the increase in the population. And where they came from.
Remember back in 2019 when Shapiro declared that the monarch population is on life support?
Hold on...
- Author: Kathy Keatley Garvey
Have you seen any overwintering milkweed bugs lately?
About a dozen milkweed bugs, Oncopeltus fasciatus, emerged from seclusion Jan. 2, 2022 in our Vacaville garden. The temperature hovered at 32 degrees that morning, but when the sun peeked out, there they were. Mating.
Little early, aren't ya, buddies? If you're waiting for the first milkweed seeds, get set for a long wait.
Jack Frost nailed what was left of most of our milkweed. So where are the colorful reddish-orange/black bugs overwintering? In our nearby cacti and succulents.
Milkweed bugs are known as "seed eaters" of milkweed, but actually they are opportunistic and generalists, according to Hugh Dingle, emeritus professor of entomology at the University of California, Davis. In a September 2019 Bug Squad blog, Dingle told us they will eat monarch eggs and larvae (milkweed is the host plant of monarchs), as well as the oleander aphids that infest the milkweed.
"Milkweed bugs will get protein from wherever they can find it," said Dingle, an insect migration biologist and author of the textbook, Animal Migration: the Biology of Life on the Move. They've been known to feed on insects trapped in the sticky pollen of the showy milkweed (Asclepias speciosa). And on nectar.
Dingle served on the UC Davis Department of Entomology faculty from 1982 to 2002, achieving emeritus status in 2003. National Geographic featured him in its cover story on “Great Migrations” in November 2010. LiveScience interviewed him for its November 2010 piece on “Why Do Animals Migrate?”
But milkweed isn't the only plant that these bugs breed and feed on. "The fascinating thing about milkweed bugs is that they will feed and breed spontaneously on Erysimum and Cheiranthus, two Brassicaceous genera that make cardenolides!" UC Davis butterfly guru Art Shapiro, distinguished professor of evolution and ecology, told us this week.
The amazing world of milkweed bugs and the plants they feed and breed on...
- Author: Kathy Keatley Garvey
The paper, “Two Centuries of Monarch Butterfly Collections Reveal Contrasting Effects of Range Expansion and Migration Loss on Wing Traits,” appears this week in the Proceedings of the National Academy of Sciences.
The researchers:
- Lead author Micah Freedman, a former UC Davis doctoral candidate in population biology and now a postdoctoral fellow at the University of Chicago.
- Emeritus professor Hugh Dingle of the UC Davis Department of Entomology and Nematology, a noted authority on migrant animal behavior
- Sharon Strauss, professor, Center for Population Biology and the Department of Evolution and Ecology
- Santiago Ramirez, associate professor, Center for Population Biology and the Department of Evolution and Ecology
What they did:
"We measured the wings of 6,000 museum specimens of monarch butterflies collected from 1856 to the present, as well as contemporary wild-caught monarchs from around the world,” Freedman said. "The major implications of the research,” Freedman said, “are that it shows (1) loss of migration can affect the evolution of monarch butterflies over contemporary time scales--dozens to hundreds of years; and (2) monarchs with large forewings are better-suited for long distance movement, and this likely contributed to their global expansion over the past 200 years.”
Their research documents how migration-associated traits may be favored during range expansion but disfavored when species cease seasonal migration. “Furthermore, it highlights the value of museum collections by combining historical specimens with experimental rearing to demonstrate contemporary evolution of migration-associated traits in natural monarch populations,” Freedman said.
Freedman worked closely with Dingle, a UC Davis entomology professor from 1982 to 2002 who achieved emeritus status in 2003. Dingle authored two editions of Migration: The Biology of Life on the Move (Oxford University Press), is a fellow of the American Association for the Advancement of Science, and a past president of the Animal Behavior Society. His research has taken him throughout the world, from the United States to the UK, Kenya, Thailand, Panama, Germany and Australia. National Geographic featured him in its cover story on “Great Migrations” in November 2010. LiveScience interviewed him for its November 2010 piece on“Why Do Animals Migrate?”
The researchers analyzed monarch specimen collections from nearly two dozen museums, including the Bohart Museum of Entomology, University of California, Davis.
The Bohart Museum, located in Room 1124 of the Academic Surge Building on Crocker Lane, UC Davis campus, houses a global collection of nearly 8 million insect specimens. Directed by Lynn Kimsey, professor of entomology and a former chair of the UC Davis Department of Entomology and Nematology, the Bohart is geared toward "Understanding, documenting and communicating terrestrial arthropod diversity," which appears on its logo; see website. (Note that the Bohart Museum is temporarily closed due to the COVID-19 pandemic precautions.)
Said Dingle: “At a time when museum collections are under pressure from a scarcity of funding, the results also show just how valuable such collections can be to evolutionary research and to the understanding of ongoing biological processes in the face of anthropogenic change.”
His comments bear repeating:
That bears repeating: “At a time when museum collections are under pressure from a scarcity of funding, the results also show just how valuable such collections can be to evolutionary research and to the understanding of ongoing biological processes in the face of anthropogenic change.”
