OE Monarch and Queen – FAQ

Many questions are asked about OE (Ophryocystis elektroscirrha). Let’s look at these questions.

Q. My swallowtail caterpillar died. Did it have OE?
A. Only caterpillars that eat milkweed can get OE. In the US, those are only Monarch, Queen, and Soldier butterflies. No other species in the US can become infected with OE.

Q. I was told to euthanize all Monarch butterflies that have OE. Should I kill them?
A. No. If all Monarch butterflies in 2013 that were HEAVILY infected with OE in:
~ the eastern US were killed, 26.3% would be killed. Over 1/4 of the eastern population would need to be killed.
~ the Gulf Coast area were killed, 83.6% would be killed. Over 4/5 of Monarchs in the Gulf Coast region would need to be killed.
~ the western US were killed, about 14% would be killed. Nearly 3 out of 20 Monarch butterflies would be killed.
~ Miami/Dade area of Florida were killed, about 90% would be killed. That is 9 out of 10 Monarch butterflies. That doesn’t count the Queen butterflies that also have OE and exchange OE back and forth with Monarch butterflies.
HOWEVER, if you bring in eggs or young caterpillars to raise in your house or classroom and they turn out to be heavily infected, we believe it would be best to euthanize them.
NOTE: that doesn’t count those that are medium to lightly infected with OE.

Q. Does Tropical Milkweed (Asclepias curassavica) give OE to caterpillars?
A. No. Studies indicate that caterpillars that were infected with OE and eat Tropical Milkweed are less damaged by the infection than those that at other species of milkweed. Tropical Milkweed prevents OE from causing as much damage to the caterpillar/chrysalis. However, like every other species of milkweed, if OE spores are on the leaves, it can give OE to caterpillars eating the leaves.

Q. Where do butterflies get OE?
A butterfly gets OE as a caterpillar when it eats a spore. Spores are spread only by adult butterflies. A caterpillar can eat spores that were left on the egg when it was laid (they eat their eggshells) or they eat leaves with spores.

Q. What kind of microscope do I need to see spores?
A 100x or stronger microscope that is not a child’s toy will magnify the spores enough to see them clearly. Click here to visit our Check For OE page to learn more. Although some toy and hand-held microscopes can show spores, if you want to know for sure whether a butterfly had OE, we strongly encourage borrowing or purchasing a better microscope. Weaker ones can show OE if you know what you’re looking for but you only see a few scales at a time. A better microscope is best.

Q. When I look through my microscope, all I see are just a few spores. Can I release it?
If you gathered the caterpillar from your garden, yes, release it. Gathering one from the wild and releasing it with OE is natural. (If you are a butterfly farmer/breeder, raising them generation after generations, even one spore is unacceptable.)

Q. My chrysalis turned black and mushy. I’m sure OE killed it.
Black and mushy indicates a different disease, not the parasite OE.

Q. How bad is OE?
Although OE normally only weakens butterflies, at the most, it does kill some before or when they emerge from their chrysalises. If caterpillars eat many spores at a young age, it can kill them as caterpillars. Nature has a way of washing a large number of spores off of leaves (rain and wind). If you raise caterpillars indoors, disinfecting the leaves with a weak bleach solution can kill spores.

Q. Why don’t all the Monarch butterflies in southern Florida die since 70% are heavily infected with OE?
Because this parasite MUST keep the insect alive or it will kill itself. OE’s very survival is dependent upon adult butterflies flying to spread spores.

Q. Freezing temperatures kill OE spores, right?
Freezing temperatures kill many OE spores but some spores live through hard freezes.

Q. My Monarch caterpillar died from OE. What do I do now?
First, it isn’t often that a caterpillar dies from OE. There is a much greater chance that it died from a disease. If OE killed it, it cannot spread. ONLY mature spores, from an adult butterfly, can spread spores. A dead caterpillar cannot. BUT since OE rarely kills caterpillars, treat the death as if it were diseased instead of infected with OE. 1) If no other caterpillars were with it, clean out the rearing container and disinfect everything that it would have touched. 2) If other caterpillars were with it and they appear healthy, move them to a disinfected rearing container and add fresh leaves. Clean out the first rearing container and disinfect it. Place all old leaves and other items from the container in a sealed plastic bag and dispose of it off site OR dig a deep DEEP hole an bury it. Disinfect the first container. With NPV, over a half billion virus particles can be in one caterpillar. It is best to get rid of everything that can’t be disinfected by disposing of it where wild butterflies can’t get to it. 3) If other caterpillars appear sick or more are dying, dispose of all contents in a plastic bag in the same manner as mentioned above. You can euthanize caterpillars by either flushing them down the toilet or placing them in a little plastic bag and freezing them. They should then be disposed of as mentioned above. Freezing does not kill virus particles and even after freezing, these pathogens can be spread.

Q. My caterpillars have spots. Does that mean that they have OE?
Spots on a caterpillar are an indicator of a problem but they are not OE spores. I’ve seen spots on caterpillars without OE and never noticed them with OE. Others have had the opposite experience. Many people tie in dark spots in caterpillars with dark spots in chrysalises. Dark spots on caterpillars aren’t an indication of spores, as many people think, because they don’t become dark spores until a couple of days before they emerge. Even in a chrysalis, dark spots the first few days do not indicate OE. ONLY the last three days before they emerge could dark spots indicate OE.

Q. My Monarch butterfly couldn’t emerge from its chrysalis. What do I do with it?
Euthanize it if it is alive. Either flush it down the toilet or freeze it. It may or may not have OE. Click here for directions to determine if it had OE. Dehydration can also prevent a butterfly from emerging successfully. Click here for more information about preventing dehydration.

Q. I was told to bleach my eggs. Won’t that kill them?
No, disinfecting eggs won’t kill them. You can see a video here with directions to disinfect eggs. Follow the recipe and instructions carefully! If you’re nervous, practice with uncooked rice. There are many good directions and recipes. This is just one of many.

Q. How do I disinfect my rearing containers?
It depends upon what type of rearing container!
1. Mix 1 part bleach with 9 parts water (and a few drops of dish soap) in your tub or sink. Submerge your clean rearing containers, taking care that all sides and parts are wet with the solution. Allow to soak for 10 minutes or more. Remove, rinse and re-rinse, and dry (drip dry is fine).
2. If the container is small and won’t melt in a dishwasher, wash it in the dishwasher on full cycle.

Q. If only adult butterflies spread spores in nature, what about my butterfly net?
Butterfly nets should be disinfected regularly. A dip in 10% bleach and 90% water for several minutes followed by a GOOD rinse will kill spores on the net.

Dr. Chip Taylor; Monarch Watch
Dr. Sonia Altizer; University of Georgia:

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