[Jacqui]

If anyone is really concerned about their monarch caterpillars dying from Oe (Ophryocystis elektroscirrha) you might be interested in this presentation.

The presentation has been put together for a North American audience, mainly butterfly farmers: people who rear hundreds of monarchs every season. In North America some people say the disease needs to be eliminated. However, Oe is as natural as the intestinal worms that cattle, sheep, dogs, cats and humans get – or the common cold. No-one in New Zealand sees Oe as a significant issue. From time to time you might have an outbreak in your garden or butterfly rearing facility so it is good to be aware about it.

Personally, I have been raising monarchs for over 50 years and one season I did have a serious outbreak of Oe. What happened was that I already had a crowded butterfly house and someone in the same town (Russell) had pulled out all of their big swan plants (because they were messy) and was taking them to the dump. I saw the back of their truck, laden with dying swan plants which were covered with caterpillars, so I rescued all of the plants and caterpillars and put them into my butterfly house.

It would just take ONE of those monarchs to have an Oe spore for it to become a problem of plague proportions and that was what happened. I had to start again: pull everything out of the butterfly house, sterilise everything, buy new plants and collect more eggs. It was a good lesson: don’t try and rescue everything.

I have posted elsewhere about how wasps and mantises and Oe prevent the monarch populations becoming too large. Monarchs prevent the swan plant from taking over the world. (see my forum post “a plague of monarchs”.

So, don’t panic… but you might want to watch the presentation to learn more about this monarch disease.

[NormTwigge]

As Jacqui points out, Oe is a natural occurrence in monarchs, and indications are that it co-evolved with the monarchs.

“OE infects monarchs in all three North American populations. The eastern migratory monarchs have the lowest infection rate. Less than 8% of these butterflies are heavily infected with OE. More monarchs have OE west of the Rocky Mountains. About 30% of the western migratory population is heavily infected with OE. The highest rate of OE in North America occurs in the nonmigratory monarchs of South Florida. More than 70% of these monarchs have OE infections. The infection rates for monarch populations in North America have been constant for many decades”. (source University of Georgia)

In Southern Florida, where the monarchs are nonmigratory, the milkweeds grow all year round, so perhaps this is a reason for the high infection rate. So does it follow that monarchs in the frost free north of New Zealand have greater Oe problems than those in the south?
“How come Oe isn’t a significant problem here? I have never seen any major outbreaks of Oe.”
Looking back on various postings on the forum would suggest that maybe it is problem, albeit a minor one, given that being a much smaller country than U.S.A, we have proportionately less monarchs.
Food for thought.

[Jacqui]

Monarchs can be naturally infected by Ophryocystis elektroscirrha or Oe.

In North America there is a huge campaign to get people planting native milkweed, i.e. native to that region. Evidently, over the years people have been planting Asclepias curassavica or tropical milkweed as it is easy to grow but it is not a native – native to central and South America. There are concerns that it is causing disruption to the migration and also spreading Oe.

When winter comes, in colder climates, the native milkweeds die down and either go into a dormant phase or grow from seed that has been scattered by the wind in the autumn. This seed is naturally hardened off in the frosts/snow and starts a new generation of plants in the spring. The Oe spores are killed.

So – it is interesting in New Zealand where the milkweed of choice is the swan plant (or giant swan plant), Gomphocarpus species from Africa, which in the northern half of the country does not die down. How come Oe isn’t a significant problem here? I have never seen any major outbreaks of Oe.

Norm and anyone else – any thoughts?

[Author]

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