What is Oe or Ophryocystis elektroscirrha?

Monarch butterflies all over the world are infected with Ophryocystis elektroscirrha or Oe. It is a protozoan parasite that is a monarch specialist. The hardy parasite forms spores on the exoskeleton (or effectively ‘skin’) of adult monarchs. Spores are clustered among the butterfly scales and concentrated mostly on the abdomen.

When infected female butterflies lay eggs on milkweed such as swan plant, parasite spores are transferred to the eggs and milkweed after which they are consumed by early instar caterpillars.
The spores then open in the gut, and the parasites penetrate the gut wall.

During the late larval and pupal stages the parasite undergoes asexual and sexual replication and when the adult butterflies emerge from their pupal cases they have a new generation of parasite spores on the outsides of their bodies. Oe causes considerable harm to monarchs, reducing pre-adult survival, adult body mass, mating ability, fecundity, flight ability, and adult lifespan.

Caterpillars that are infected with a single parasite spore can metamorphose into adults carrying over one million spores!

Unfortunately, there is nothing that can be done to cure or fix butterflies suffering from this disease. The only way to stop the parasite is to ensure food plants do not become infected with spores, which is almost impossible for plants maintained outside. A healthy-looking, but infected butterfly flying in from your neighbour might introduce the parasite.

If you rear caterpillar in greenhouses or cages you could try to ensure any females that are used to lay eggs have no pathogens. It is possible to decontaminate cages and other equipment by soaking them in a 10% bleach solution.

The healthiest monarch butterflies have been thriving without our help for millions of years. Overcrowded conditions are not seen in nature. Saving unhealthy caterpillars and butterflies is not helping monarch butterflies.