My 2023 Monarch Raising Project (III: Disease)

[During the spring of this year, I hope to raise and release 240 monarchs. This is the third post in a series about my monarch butterfly raising project. The first post in this series dealt with growing milkweeds, the host plants for the monarch butterfly. The second post dealt with native flowers to attract the butterflies. This post is about dealing with the possibility of disease.]

In order to raise and release 240 monarchs butterflies, I will need to grow a large amount of milkweed in a fairly small space. I will also have too rear the butterflies in close quarters inside my butterfly enclosures. Anytime any species is found at a high density, the possibility for a disease to spread through the population is present. 

In order to minimize the possibility of a disease outbreak, I will need to do two things — monitor the plant and butterfly populations for diseased individuals and isolate them. It would be great if I could prevent all of the diseases that affect milkweeds or monarchs from arriving, but that isn’t possible. Insects arriving in the garden bring many diseases. Spraying insecticide to kill these insects is not an option because that would also kill the monarchs. Likewise, netting the plants would keep insects off them, but that would include the monarchs. So, I can’t prevent the arrival of insect-borne diseases. With that being the case, I need a plan to deal with insect-borne diseases, should any arrive. I can prevent fungal diseases by avoiding overhead watering and pruning the plants to increase airflow around them, if needed. 

One piece of good news is that I’ve never had a problem before. By the end of every season, my milkweeds are infested with milkweed aphids and milkweed bugs. And sometimes, their leaves get a bit mottled (suggesting some sort of disease). However, every spring the milkweed returns and is healthy. I’ve also never detected any problems with disease among the monarchs. I’ve had tachnid fly infestations, but I deal with that by raising the caterpillars in netted enclosures. 

My plan for dealing with disease is to monitor the plants and the butterflies (larvae and adults) for potential problems. If I detect a problem, I will isolate (or destroy) the diseased individuals. If a plant looks ill, I can simply remove it from the garden — hopefully before whatever it had spreads to other nearby plants. Likewise, if I see a caterpillar that looks ill, I can remove it from its enclosure and not add any new monarchs to that enclosure. I have several, so I can rotate through them and sanitize used enclosures before using them again. 

To make disease less able to spread quickly, I will also physically spread out my milkweed plants as best I can. This may not help much if an insect-borne disease arrives, as insects could easily fly from one side of my yard to the other. But it will help with any disease which spreads faster with physical proximity. I will also raise the monarch caterpillars in as many different enclosures as is feasible. That way, if an individual becomes diseased, the disease could only be spread within its enclosure — which could be sanitized before being used again. 

Other than tachnid flies, one of the biggest threats to monarchs is the protozoan Ophryocystis elektroscirrha (often simply referred to as OE). Given the seriousness of OE, I’ll devote an entire post to how I will deal with this, should it arrive in my garden. One of the major things gardeners can do to avoid an OE infestation is not grow non-native milkweed. All of my plants are natives, so that’s not a problem. But, the disease is still worthy of serious consideration. 

At the time I am posting this, it is about 5 weeks away from the milkweeds sprouting and maybe 6 or 7 weeks from the monarchs arriving at my garden in central Texas. I have a lot of milkweed seed cold conditioning (stratifying) right now and I also have several milkweed rhizomes in my refrigerator. These are in addition to the milkweeds in my container garden planters. Things should start heating up in early March. If you’re interested, I hope you follow me on my quest to 240.