Creating a wildlife haven one plant at a time

Wednesday, February 13, 2013

OE & Monarch Conservation

This winter I have attended several talks on the conservation of the monarch butterfly which has opened my eyes further to the importance of gardening with native plants and creating native habitat to help conserve these iconic insects.


If you garden for butterflies you probably have milkweed to attract monarchs and a variety of other butterfly species. Recent studies have shown that planting non-native milkweed is detrimental to the Monarch butterflies. Why you ask? Well, there is evidence that the non-native milkweed species are changing the migration timing of Monarchs. The tropical milkweeds have longer bloom periods and encourage Monarchs to stick around instead of continuing on their epic migration. By lingering they are put at risk of the deadly OE parasite and also at risk of dying in our winter.

What is OE? Ophyryocystis elektroscirrha (that is a mouthful!) is a parasite that infects monarch and queen butterflies. It is a protozoan or single celled organism that must live within a host to grow and multiply. Between infections it lives as a spore and can survive extreme environmental conditions.

OE was first found in the 1960's in Florida and as far as researchers have discovered the monarch and queen butterflies are the only known host. Over the years OE has been discovered in monarch populations world-wide and the research is showing that OE has co-evolved with the monarchs. You can see in the diagram below the life cycle stages of OE in the monarch. You can click on the photo credit below for a larger view.

Photo courtesy of monarchparasites.org

OE only reproduces in the butterfly's body. According to Monarch Watch spores can be transferred from an infected male to a healthy female during mating. Infected females also pass along OE to their offspring. When the female lays her eggs, dormant spores are scattered on the eggs and milkweed leaves. When the caterpillar emerges from the egg the first thing it will eat is its eggshell and then begin munching on the leaves thus ingesting the spore.


Most butterflies with mild infections look and act normally but they are usually smaller than healthy adults, weighing less and with shorter forewings. The only way to know for sure is to test for the parasite. Volunteers can participate in this process by collecting samples from monarch butterflies they see in their garden. (More information on participating is provided at the end of this post)

Heavily infected butterflies often die before emerging from their chrysalis. If they do emerge they are weak and often fall to the ground before they can expand their wings. These butterflies do not survive long.


In North America the populations of monarch butterflies are divided into three groups. The Eastern where the monarchs breed east of the Rocky Mountains and overwinter in the transvolcanic mountains in central Mexico. The Western population which are west of the Rocky Mountains where the butterflies roost along California's coast and finally the Non-migratory which breed year round in southern Florida, coastal Texas, Hawaii and the Caribbean. Of these populations the Eastern population is the least heavily infected at 8%. The Western population is at 30% and the Non-migratory group is the highest with 70% of the population heavily infected with OE.

photo courtesy of Project Monarch Health Watch

So, this begs the question, what implications does the monarch migratory behavior have on the occurrence of OE? Well, new research at the Altizer lab at the University of Georgia has shown that migration allows hosts to escape infected habitats reducing disease levels. Diseased butterflies lost more of their body weight during flight and therefore would not survive the long migration to Mexico thus weeding out the parasites with them. Non-migratory populations retain their weakened butterflies and so the parasites persist. Researchers also found (in a 2010 study) that wild monarchs in the non-migratory populations were smaller. The Eastern population had the largest and most elongated forewings and largest bodies.


So what does all this mean for the average butterfly gardener? To best support healthy monarch populations it is best to bring into cultivation milkweed seeds from local sources. Migrating monarchs have co-evolved with the native milkweed, timing arrivals and departures with bloom periods over many generations. There are 22 milkweed species native to Georgia and for a complete list and plant profiles click here.

If you are so inclined you can participate in the Project Monarch Health which is a citizen-science survey where volunteers sample wild monarch butterflies to help track the spread of the OE parasite in North America. This is great activity for backyard gardeners, school groups, nature centers, senior groups and is done by people of all skill levels and age groups.

27 comments:

  1. Very informative post, I was not aware of OE. I have given up on tropical milkweeds in any case because I found them disappointing as ornamental plants. I do have plenty of swamp milkweed, plus some butterflyweed and purple milkweed. I'll be planting more butterflyweed in the spring.

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    1. I tried tropical milkweed years ago since that is what the big box stores carried (I don't shop them anymore). They are annuals in my neck of the woods but they will bloom long into late fall until we have a frost. It can be difficult to find native milkweeds but our native plant society and nature center sell them and many local nurseries do now too. Ironically the common milkweed isn't so common in Georgia. I see much more of it when I visit my family in Michigan, growing along roadside ditches.

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  3. Good information, Karin. I also went to their link. It seems that more and more insects are being exposed to killing parasites or infected by virus and fungus. It really makes sense on the fact that Monarchs are migratory and the would lessen the parasite infestation by weeding out the weaker butterflies.

    Having bees travel long distance was recently noted in bees as a factor in CCD, but in an opposite fashion. The Science report noted honey bees being farmed, got new infection when they traveled out of their native areas. Traveling long distance also lowered their resistance too. The study looked at native bees and their resistance to many factors making up the CCD symptoms. They also noted that being solitary, the bees were less likely to have the disorder. I wonder how that will change thinking on butterflies, whether migratory, or non-migratory.

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    1. It is fascinating all they are learning and yet it doesn't seem fast enough. I know they are doing a lot of research here at the University of Georgia on the monarchs under the leadership of Sonia Altizer whom I had the privilege to hear speak about monarch behavior and interactions with the protozoan parasite. It will be interesting to see what the next few years of research tell us about the bees and butterflies!

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  4. This is good information to know. I don't currently grow any milkweed, but have been thinking about adding some. I now know to research our natives and only grow them. Thanks for this informational post!

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    1. Milkweed are great plants and attract lots of different butterflies. They are not only host plants for monarchs but also queen, coral hairstreak, spring azure and sleepy orange butterflies so in my book you can never have enough milkweed :)

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  5. I learned a lot from this post, as I wasn't aware of OE either. It's a rough world out there for some of our pollinators. I do grow a native narrowleaf milkweed here, although we're more in the Monarch's wintering area, than breeding area here.

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    1. I am mostly familiar with the monarchs we have here that migrate to Mexico for the winter. What is their behavior on the California coast for the winter months?

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  6. You've shared so much important information, Karin. I planted swamp milkweed several seasons ago but it never flowered and I pulled it up at the end of last summer. I hope to replace it with another native variety. Thanks for the great post!

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    1. Swamp milkweed is a native milkweed to Georgia. I planted some last year but they do like more moist soil and sunshine and the mostly moist soil we have doesn't get much sun so I'll see if it comes back this year.

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  7. I didn't realize the tropical Milkweed was being sold at garden centers. Actually, I haven't thought much about Milkweed except as a wildflower. I don't have any here, but I see it a lot out along country roads. Good to know about the Milkweed, OE, and the monarch migration patterns. Thanks, Karin!

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    1. I is an annual and it has been sold at garden centers the past few years here in Georgia. I see a lot of the common milkweed along the roadsides in Michigan and I imagine your area is similar. The problem is all too often these roadsides get mowed at the wrong times and then the seeds don't have time to disperse and there is a big decline in their habitat.

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  8. I have quite a bit of asclepias tuberosa and incarnata but none of the tropical milkweed. I'm glad to see both of them on your list. You can buy trays of 38 for $92 from Prairie Moon Nursery in MN. I've had monarchs linger for too long in my garden in the fall and wondered if they made it to Mexico. Thanks for this info. I've bought the tropical milkweed in the past but will resist it next time. :o)

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    1. Thanks for the info from Prairie Moon. I am starting some milkweed seeds indoors right now to put out in spring. Have you ever participated in the Monarch tagging program? It could be a fun way to see if your butterflies make it to Mexico. One tip that Sonia Altizer mentioned for people who insist on growing tropical milkweed (particularly those who live in coastal areas where they can be perennial) is to cut them back in the fall.

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  9. I love finding out more about my beloved butterflies...I only have native milkweeds and I am hoping for a bumper crop of butterflies this year. Fabulous post Karin!

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    1. We had our largest Monarch count last fall. Hopefully we will see even more this year. I hope they find your garden and your meadow with all the goodies!

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  10. Very interesting. Common milkweed grows wild all over our farm, but what I really see the Monarchs going for is the Swamp Milkweed. Especially 'Ice Ballet', they really love that one.

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    1. It is interesting how they have their favorites! Good to read that they really like swamp milkweed. I have heard that monarchs are really attracted to the tropical milkweed and I assume it is because it has very high levels of cardenolide. Unfortunately, this makes it tempting for gardeners to plant. The butterfly weed has lower cardenolide levels than other milkweed species. However, I have found caterpillars and butterflies on my butterfly weed every year.

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  11. A very important post that reminds us how important it is to pay attention to these details. I only have one milkweed plant with plans to add more, but I have made sure these are native. I do have other plants that they like even though milkweed is good for their reproduction. Great post!

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    1. I have been adding more milkweed each season. I hope more monarchs will find my garden and tell all their friends!

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  12. Great post Karin, there's lots of good information here. I had never heard of OE before. I've been considering planting milkweed on my property and this really solidifies that decision for me. Would you believe some people have advocated not planting native milkweed because they say it's invasive? It grows with wild abandon for sure but it's NATIVE and that to me is not invasive.

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    1. So interesting that you mention that...in class today on Natural History of Georgia plants we discussed definitions of natives and invasive. There are multiple definitions depending on who you ask. I've never heard of milkweed being classified as invasive. In most places milkweed habitats are destroyed especially with current farming practices and introduction of GMO crops. So many insects need milkweed to survive I think the more the better. Good for you for planting some!

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  13. Karin, you post was very informative. I don't grow milkweed. I'm not sure if I've seen it in the big box stores or nurseries in Santa Fe. For the last few years, I've been buying native plants and my garden seems to be much happier. I buy my plants at local nurseries, but it's too bad that big box stores don't sell more natives for people who can't afford to go nurseries.

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    1. Isn't it amazing what a difference adding native plants makes to attracting wildlife to ones garden! I prefer to support local nurseries too. I think the quality and selection is so much better. Big box stores carry what sells and often that includes invasive plants that look attractive so people buy them that don't know better. Plus I find that the people that work in the box stores don't know much about gardening either. They can read the tag (which is often wrong) and that's about it.

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  14. I had no idea about the parasite. Wow. Great information Karen, will head over to the Project Monarch Health site.
    Would you believe that ALL my coneflowers have been eaten from below ground? Other plants are fine, but every Echinachea is gone and there is a hole with a small remnant of the last flower stalk going down the hole.

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    1. Oh no, it sounds like the voles have been busy! They must have had a flu outbreak this winter, LOL!

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