Monarchs and OE Disease

I came across Dr. Mark Hunter of the Univ. of Michigan and his Hunter Lab website and their interesting research of Monarch butterflies, the protozoan parasite – Ophryocystis elektroscirrha (OE), and climate change. I asked him a number of questions and he was nice enough to answer them – here are his answers.

1. 1) How deadly is OE to Monarchs. Obviously it’s not 100% fatal, but I’m wondering what the percentages are?OE is not usually lethal to butterflies.  Most survive the disease.  But I’ve seen up to 20% mortality if the butterflies have some other source of stress. But, in most circumstances, it doesn’t kill them.  But it does cause large reductions in lifespan and in birth rates.  So the disease can have significant impacts on monarch populations by reducing the number of eggs laid each year.
   2) Apparently Asclepias curassavica helps survival, but doesn’t that just spread the disease even more? Your comment about Asclepias curassavica helping as a medicine, but increasing disease spread, is very astute.  It has great medicinal properties, but should not be used as the only source of food for butterflies.  This is like putting all of our kids on antibiotics from birth onwards – all it does is select for virulence in the parasite.  So we would end up with parasites that are much worse for the monarchs.
   3) Have you seen any data to show that Monarchs are developing any sort of resistance to this parasite? There is evidence to suggest that there is some variation among monarch populations in resistance.  But the disease occurs world-wide, and there are no fully-resistant populations.  In general, parasites evolve faster than their hosts, so they usually overcome host resistance at some point.
   4) Since Monarchs have lost most of their Common Milkweed farm habitat, I’m looking for the best milkweed alternative for the home gardener. I always encourage people to plant a diverse group of milkweed species, native to their own location.  This way, we let the butterflies choose what they need when they most need it.  If you let me know where you live, I can make some recommendations for particular species.  Here in Michigan, I recommend a mixture of syriaca, sullivantii, tuberosa, exaltata (if you have shade) and incarnata (if you have wetter areas).  But the key is to plant a mixture so that the butterflies get a choice and we don’t select for virulent parasites.

Below is a video on some of the research he is doing.