Testing for the OE parasite
"OE" is short for Ophryocystis elektroscirrha, a microscopic parasite found in all monarch populations. Like any parasite, it doesn't usually kill monarchs. However, infected chrysalids may have difficulty eclosing, which sometimes results in death or deformed wings. More often, an OE infection just weakens adult butterflies, so they are less likely to complete the migration. This means that migratory populations of monarchs have a lower % of infection. In our eastern migratory population, fewer than 8% of monarch adults are infected. See Wikipedia.
The OE life cycle
The infection is spread by tiny spores, visible only with a microscope. Infection begins when a caterpillar ingests a spore attached to its eggshell, which the caterpillar eats immediately upon hatching. It can also become infected by eating a spore on the surface of a milkweed leaf. Once eaten, the OE multiplies within the caterpillar but does not cause any symptoms. The parasite multiplies further within the chrysalis, where it produces spores.
Three days before eclosure, you can see accumulations of spores through the transparent shell of the chrysalis--it looks mottled with dark patches. Other signs of infection are difficulty eclosing, deformed wings, or a smaller size (or wingspan).
The majority of the spores are fond on the abdomen. The abdomen of an uninfected adult has crisp white and black stripes. If heavily infected and covered with dark spores, the abdomen may look more "dirty or dingy."
The amount of infection varies--it's more severe if a caterpillar ingests more spores, or if the infection occurs earlier in the caterpillar's growth. So adults can be heavily infected and less fit, or lightly infected and nearly normal.
A heavily infected male or female can carry tens of thousands--maybe even millions--of spores on its body. As they fly about, they scatter spores around the environment and onto milkweed leaves. When an infected female lays an egg, one or several spores may stick to the eggshell.
Because of the huge number of spores an infected adult can scatter about, you have to assume your equipment is contaminated if it has been around or held adult butterflies. If a mesh tent is used to hold butterflies, it must be disinfected before you can use it for caterpillars.
Summarizing, your caterpillars may become infected because they ate a spore...
- stuck to their eggshell when the egg was laid.
- dusted onto a milkweed leaf found in the wild.
- contaminating your hands or equipment that wound up on milkweed food.
Although the <8% infection rate isn't especially large, once OE gets introduced into your raising or breeding operation, OE could spread to all your caterpillars (and then butterflies) if you aren't careful. If you are just raising caterpillars, the most important thing is to sterilize with bleach any container that has held adults before you use it to hold caterpillars. Likewise, use hand sanitizer after handling butterflies.
How to test adults for OE
If you are breeding adults to produce eggs, you must test all the females that are laying eggs to make sure they are free of OE. To save time, you need only test them once they have laid their first egg.
Supplies needed
Disposable gloves
Hand sanitizer
4x6 cards
Transparent tape with clear, not frosted surface
Microscope with 100 power
Small flashlight
A sample from a butterfly infected with OE (to train your eye)
Taking a sample
First, you need to take a sample by pressing the sticky side of the tape against the female's abdomen. We'll assume you are right-handed. First, cut a piece of tape about 1 inch long, or slightly shorter, and temporarily stash it by sticking a corner of the tape onto your knuckle or little finger.
Hold the butterfly with your left hand, pinching the two wings together, so the abdomen is fully exposed. If the abdomen is still obscured by the lower wings, you can gently pinch the lower wings on both sides together until the abdomen is forced out into the open.
Next, shape the tape into a shallow U-shape with the thumb and forefinger of your right hand. Now press the sticky side of the tape against both sides of the abdomen, and pinch lightly with thumb and forefinger so the abdomen is slightly flattened by the pressure. The goal is to make good contact of tape to abdomen. Now peel the tape away and stick it, sticky side down, onto the middle of the 4x6 card. Release the butterfly back into the tent. Immediately write the butterfly's number onto the card and place the card in a fresh zip-loc bag.
This all requires some dexterity but here are a few tips to make it easier. First, if you are gentle, you aren't going to hurt the butterfly by squeezing its abdomen just a little. If you have a helper to hand you things like the freshly cut tape, then the card--that helps (but it's possible to do it alone). That person also has to avoid contamination. When I squat in the breeding tent, I brace my forearms against my knees to steady them. Probably the hardest part is getting the U-shaped tape bent, then positioned in your right hand, then pressed onto both sides of the abdomen. You might get the tape shaped/positioned in your right hand first, with help from your left hand, then grab the butterfly with your left hand. You can also practice these moves before involving a butterfly.
How to ensure a clean sample
The most important thing--I can't overemphasize--is to get a sample free from contamination from other sources. Let's say you have several females in your breeding tent, and one of them is heavily infected. There are OE spores everywhere! You want to make sure that when you take a sample from an uninfected female, you aren't inadvertently getting some spores that were contaminating everything.
Most experts recommend you use fresh disposable gloves to take each sample--but I find the gloves interfere with my manual dexterity, so I use an alternate method.
I wash my hands thoroughly between sampling different butterflies, and after touching anything. I keep all equipment and supplies away from the breeding tent. I keep the tape and cards used for sampling enclosed in zip-lock plastic bags, always zipped shut. When I draw a piece of tape just before sampling, I make sure the piece came from contacting the roll of tape and wasn't exposed to the air until just before it was cut. Hands, tape, and card must be completely clean.
Observing the sample with a microscope
Use a microscope with 100 times magnification with an attached light. You can supplement this light with a flashlight shining from the side if needed.
In the sample, you will see large butterfly scales that look just like oval feathers, colored black, white, or sometimes orange (from the wings). The scales are in two patches, one patch from each side of the abdomen. You may see some scattered particles of pollen, dust and debris that are much smaller than the feathers. Some of this small debris is inevitable--it was on the butterfly--but hopefully minimal if you have been careful to avoid contamination.
What you are looking for--the OE spores--are tiny, about 1/100 the size of a scale. Their distinctive football shape is most diagnostic. Pollen grains can be the same size and take a variety of distinct shapes, but I don't recall ever seeing one that was football-shaped. If you can get higher magnification, you may see some additional details, such as ridges that run lengthwise, or slight pits (depressions) in rows between the ridges. The regular, smooth and crisp football outline sets them apart from ever-present dust and debris which has random, fragmented shapes. This dust is composed of fragments of vegetation, cells, and soil.
OE spores are most likely orange but can be brown or black. Sometimes they are just uncolored clear outlines of a football (if they have died and dried out). Some debris can also be orange, but it has the random or fragmented shape.
The OE spores tend to occur in clusters (such as 10, 20, or 40), but you can see as few as one or two, or thousands in a heavily infected butterfly.
In the photo, the large grey oval (lower left) is a butterfly scale. All the other objects, much smaller, are OE spores.
Move the sample about and look at least 6 different spots, three from each side of the abdomen. Record on the card how many of the places you look at have OE. Record if you see clustering. If you see just isolated football shapes, record roughly how many. I consider a few isolated footballs to be contamination from another nearby butterfly that has been housed in the same container. But clusters, especially more than one cluster, are a definite sign of infection. Record the time, date, person who did the sampling and diagnosis, and conclusion (OE positive or negative).
