We often wish we could eliminate OE (Ophryocystis elektroscirrha) from nature. It can’t be done. Why?

Before we discuss why, let’s first emphasize that we should do all we can to keep our rearing areas clean of OE, disinfect milkweed leaves before feeding them to caterpillars (especially if we live where there is a higher OE incidence), and disinfect eggs we bring in to raise. This goes for enthusiasts as well as butterfly farmers. Always emerge adult butterflies AWAY from caterpillars and their food.

OE is in nature and there is nothing we can do about that fact. (As butterfly enthusiasts and farmers, we can raise butterflies and not increase the OE incidence in the wild. That isn’t the topic of this webpage. To learn more about raising OE free butterflies, visit this linked page.)

OE is simply part of the Monarch world. It has been found in several continents, islands, and countries. These include North America, Hawaii, Australia, New Zealand, Cuba, Central America, and South America. It has been found in Monarchs, Queens, and the Plain Tiger (the last is not found in the US). That’s Danaus plexippus, Danaus gilippus, and Danaus chrysippus.

Why can’t we eliminate OE in nature?

Stop and consider these facts:
1) it is estimated that at least 1/3 of Monarchs in the US have OE to one degree or another
2) all Monarchs in the Miami/Dade area are considered infected with OE
3) most likely nearly all Monarchs in Mexico are infected with OE
4) the parasite is found in many countries and several continents and islands
5) Queens in the US and Mexico (at least) are infected with OE
6) OE will transmit from one species to another
7) OE has been found in 3 Danaus species and suspected to be in more
8) Millions of Monarchs from the Eastern US, Eastern Canada, and some from the Western US migrate to Mexico, intermingling with each other during winter months. Many are OE infected. When they begin to mate in the spring, one without OE will often mate with one with OE. This will transfer spores to the outside of the uninfected butterfly where they can be transferred to milkweed leaves, another Monarch, and milkweed leaves. (Cross-transfer causes few problems compared to direct infection.)

Let’s look at the life cycle to learn more about it.

OE is a protozoan parasite that depends upon the host to survive. Only a caterpillar can ‘get’ OE. It eats a spore that was left on milkweed leaves or an eggshell by an adult butterfly. Once it eats the spore, it breaks open it the caterpillars’ gut. Inside the spore are OE sporozoites. They move to the hypoderm (just under the skin/cuticle) and begin to duplicate.

At this stage, it is not contagious to other caterpillars. The sporozoites continue to reproduce and multiply inside the caterpillar. This means that the earlier the caterpillar eats a spore and the more spores it eats, the more sporozoites will be in the caterpillar. Sporozoites are the living active OE organisms. They do the damage that weaken and, in extreme cases, can kill the butterfly.

When the caterpillar pupates, the sporozoites continue to reproduce and multiply. Three days before the adult butterfly will emerge, the sporozoites begin to form spores in the chrysalis. Spores are simply a hard casing containing sporozoites. When a caterpillar eats a spore, the casing dissolves and the sporozoites are released.

Before the adult emerges, all OE sporozoites in the chrysalis/butterfly have moved to this layer, just underneath the skin, and have made spores. When spores are made, they are made just below the skin/cuticle. Stop and think about this. The body, other than the area just under the skin/cuticle, is free of OE sporozoites. Spores are formed just under the skin/cuticle.

When the adult emerges, it leaves behind the outer skin/cuticle and at this point, microscopic spores are on the OUTSIDE of the butterfly. Remember that when it was a chrysalis, all the OE was located in that layer. That means that when it emerges, no OE is left INSIDE the butterfly. Only the outside of the butterfly has spores. If the caterpillar ate a spore when it was near pupation, it would have a light infection with few spores. If it ate a spore earlier in life, as a young caterpillar, it will have more OE spores when it emerges.

If it eats too many spores at too young of an age, it can be crippled or it can will die.

Spores are all over the outside of the butterfly and come off as it flies. Spores especially come off the adult butterfly as it lands on plants (milkweed and nectar plants) and sticks to eggs as it lays them.

As a caterpillar eats its way out of the egg and eats its eggshell, it may eat one or more spores. As it eats milkweed leaves, it may eat one or more spores. A butterfly can only become infected with OE by eating one or more spores as a caterpillar.

As an adult without OE, it can become contaminated with OE spores by mating with an adult with spores or touching (or being touched) items with spores. For this reason, it is important to disinfect butterfly nets and butterfly cages/habitats if you tag and/or raise Monarch or Queen butterflies.

NOW that the life cycle is explained, let’s look at this again.

1) it is estimated that at least 1/3 of Monarchs in the US have OE to one degree or another
2) all Monarchs in the Miami/Dade area are considered infected with OE
3) most likely nearly all Monarchs in Mexico are infected with OE
4) the parasite is found in many countries and several continents and islands
5) Queens in the US and Mexico (at least) are infected with OE
6) OE will transmit from one species to another
7) OE has been found in 3 Danaus species and suspected to be in more
8) Millions of Monarchs from the Eastern US, Eastern Canada, and some from the Western US migrate to Mexico, intermingling with each other during winter months. Many are OE infected. When they begin to mate in the spring, one without OE will often mate with one with OE. This will transfer spores to the outside of the uninfected butterfly where they can be transferred to milkweed leaves, another Monarch, and milkweed leaves.

Sources:

http://monarchparasites.uga.edu/whatisOE/

http://www.monarchwatch.org/biology/control.htm

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