Steve, could you cite the forum message you refer to above (Murray recently...); I looked back through Sept and didn't see anything obvious.

The milkweed debate is a very interesting topic and I learned a lot by poking around the Web. In my opinion, the subject falls into the category of information overload; the choice of milkweed plantings by the average butterfly gardener or even the collective of them will not significantly affect the monarch species or their migration.

Of course milkweed species vary in toxicity. These species and their potency vary along the migratory routes. Do highly toxic exotics among low-toxicity natives harm larvae or adult? There are so many other factors for monarch predation besides chemical protection from use of milkweed.

There is always the possibility of exotics out-competing the natives and becoming a nuisance to the general landscape. This is a hot environmental topic and could be a reason for invoking the popular monarch and non-native milkweeds in another attempt to discourage exotic plantings.

Hopefully someone with more direct knowledge will weigh in.

The following links are of interest:

chemicals per life stage and various predations

California forum discussion Feb2007

OE spores and milkweed species

scroll down to last paragraph for this one

This is something I've wondered about myself. Although I have a number of tropical plants because they look nice, I've always fed my cats the native that is found in the pasture around my house. It's easily collected and there is lots of it.

A study done without a preconceived answer before it started would be nice.

I'm not sure how much thought I would put into the thread Larry posted about a local nursery that sells plants telling local people to only use local plants. Major conflict of interest. Or did I read it wrong?

randy

Hello All;
Actually there has been extensive research on the toxicity of Asclepias species and monarchs. Monarchwatch.org has lots of information. Also, you can use Google scholar to find a lot of it.

A. Curassavica actually imparts one of the highest toxicity levels to monarchs and may give some protection against OE (see monarchparasites.org). In reality though the concentration of toxic cardenolides is loosely correlated to the concentration sequestered by the monarch larva. Monarchs seem to be able to sequester what they need to some extent. There are other issues with milkweed as well that effect survivability of the larvae. A. tuberosa actually is not the best to raise caterpillars on. Research shows that the larvae grow slower on it. It's theorized that the leaves of A.tuberosa is drier than other milkweeds and this makes it harder for the larva to utilize the nitrogen in the plant (if I read the study correctly). Other issues include how much latex the plant produces. Some such as A. syriaca produce copious amounts of latex that can kill 1st instar larva at high rates. I wouldn't worry too much about what you plant to raise monarchs. I certainly would not worry about A. curassavica. It is a good plant for the monarchs. I would only worry about it if it is invasive (which it may be in California). Probably one of the first generations from Mexico feed on it on the way north. There are many other species of Asclepias that are native that Monarchs use. Certainly they are worth exploring as well.

Good luck,
Elisabeth

Hi Steve et al, (is that right by the way, or did I just pull that out of a hat?)

I had no idea that I was bringing up the question at all in my remark about A. tuberosa. I was only mentioning that I heard that A. tuberosa was not as toxic as some of the other popular milkweeds and that I had never been able to get it to grow anyway so I gave up on it years ago. I wondered whether you had it growing yourself or whether you might have been confusing it with curassavica which I have all over the place.

But the question you raise is interesting though I have no knowledge of the subject and never thought about it until you mentioned it above. At this point I wouldn't lose any sleep over it at all since it seems to be used by so many people successfully with monarchs for years. But monarchs are not as easy to rear for me and I think they are susceptible to so many forms of predation that I often leave them outside when I find them because I hate to see things die. But if there is truth to the allegations about native vs. non-native I would definitely like to know.

I grow two species of native milkweed but to be honest with you they are a real pain because they appear too late for the spring migration and often go dormant before the fall migration. So what good is that. So I just have at least five or so species and let the adult butterflies pick out their own choice. They definitely choose the physocarpa and curassavica over any of the others.

As far as the notion that A. tuberosa might be invasive out here in CA, I seriously doubt it because tuberosa likes rich and well-drained soil and the only place you would find that out here is in bags at the local nursery and it's quite expensive. I doubt most tuberosas could afford it. On top of that tuberosa does not do well in pots or so the mail order catalog indicates. At least it never worked for me.

Well, I suppose it was one of those fortuitous mistakes. :)
I definitely didn't mean to imply that you thought non-natives were bad-- I simply thought you were asking the question. Still, seems to have been useful.

One of the odd things I've recognized from the last few posts is that it's not the toxins people seem concerned about, but rather this OE spore that the milkweed hosts. One person gives the link to the study that shows how certain non-natives species of milkweed increased the likelihood of infection because they doesn't die back in winter, but another poster states that it actually helps build up a sort of immunity to it.

Mostly, it sounds inconclusive and difficult to figure out. :(

Also, Murray, I'm still hoping to get some of the cuttings of willow and milkweed if I can. I've got some yarrow that I divided and put in pots for you.

Sounds fantastic to me and the willow is of course, still here so that is no problem. In fact, I may take a few cuttings myself and see if they will set root for you in the meantime. That is if I can get it together enough to remember. I hate it but sometimes I am so absent-minded. It reminds me of the post someone put up recently about the Black Swallowtail chrysalis that was losing its grip. My thought was "welcome to the club little fellow".

Have you ever checked out "Annie's Annuals" website? I am thinking of making a trip down there soon to check out some of the milkweeds and buckwheats she has on her site. It's not like it's a million miles away but I get very immobilized by the time change and the dark. I am embarrassed to admit it but I think I am dealing with seasonal depressive disorder (or is it seasonal affective disorder?). I can't seem to get enough light even in my house. I am getting disgusted with the whole subject of conservation if it means living in the dark.

Has anyone ever tried the disinfectant spray that has been mentioned on some of the monarch websites. It is advertised as a remedy for some of the diseases common to monarchs. It wasn't cheap but if it works I would be willing to try it. It was advertised as effective even if sprayed directly on the infected cat. I think I saw it last year or so. Murray

This summer, female Monarchs laid eggs on all 4 species of Asclepias growing in my yard, A. tuberosa, incarnata, syriaca, and curassavica. Of the four, A. tuberosa seemed to be used the least. I found lots of eggs and small cats on the syriaca, but there seemed to be a very high predation rate on these plants, because the cats would disappear and I didn't observe any that made it to the later instars.

I only had a few A. curassavica plants, and the Monarchs seemed to like it just fine From what I've read, this species has a high glycoside content that is good for the caterpillars. The cats ate down the plants so I only got a few flowers and they were killed by frost before they could form seedheads. It would probably grow better in a climate with hotter, longer summers. Next year I'm going to grow more of it and try to plant it out earlier.

In a warmer climate where A. curassavica is perennial, perhaps it should be cut it down each year, as suggested in the study that Larry-gene linked to above, to reduce the chance of OE spores building up on the leaves and provide fresh foliage for the Monarchs. This might have the additional benefit of helping to control aphids on the plants.