When you raise Monarchs then chances are you have heard the words parasitoid and parasite before. What are they? Are they something specific just to Monarchs? Why are they such a ‘bad’ thing? Read on, and you will soon understand…
Parasitoids are specialized insects that lay their eggs on other insects. Parasitoid larvae slowly eat their prey from the inside out…(eeeew!! Can you imagine that one?), eventually (usually), emerging from the now dead prey either as a fully-formed adult or as a pupa. If you have had a Monarch chrysalis drop silky, jelly-like threads down to the ground and then little brownish ‘pellets’ fall from it, then you have witnessed this firsthand with the Tachinid Fly.
With Monarchs, Tachinid Flies and Braconid Wasps are pretty common parasitoids. In Southern California, I’ve seen more Tachinid Flies than Braconid Wasps prey upon the Monarch larvae. The predation occurs during the larval (caterpillar) stage. The Fly/Wasp will ‘sneak up’ on the caterpillar to oviposit. The mental image is enough to give this editor the heebie-jeebies.
A parasite is a micro-organism like a bacteria or virus or even a larger organism like a mite or fungus that completes either all of most of its entire life-cycle within its host (in this case, the Monarch). Not all parasites will kill their host but all have a negative effective on the life of the host. In other words, the host does not have much chance for survival once the parasite has had its way with it because the host is now weakened.
Some known parasites that Monarchs are prone to include Ophryocystis elektroscirrha and the Pseudomonas bacteria. The Oe protozoan can be easily detected under a light microscope and in fact, many Monarchs may actually show physical signs of infection early on.
Parasites are an ‘infectious disease.’ For example, a Monarch that has been infected with Oe has dormant spores throughout the scales on its wings as well as on its abdomen. As it flies, lands, and nectars on flowers or oviposits, it scatters diseased spores onto Milkweed. As larvae grow and eat, they ingest the spores which then germinate within them, and begin their own life-cycle within their new host, the unsuspecting caterpillar.
Special Note: Once a Monarch has been infected by a parasite/parasitoid, it will NOT recover or get better! Sadly, the damage has been done, and in order to halt the progress of parasite/parasitoid, the adult must be destroyed. In the case of Oe, the spores only develop when eaten by another caterpillar.
With the Pseudomonas bacteria, the Monarch dies a nasty death. In fact, there's even a name for it…Black Death. The look of this larva speaks for itself. The bacteria can kill during the larval or pupal stage.
Everyone has probably had a chrysalis at one time darken, thinking, "My Monarch is about to eclose!" only to find that days and days later, the butterfly hasn't emerged. Instead of giving up, you wait and wait, only to find that the chrysalis actually is a deep, dark black that then perhaps bursts with a putrid odour followed by a nasty mess of diseased...well, let's not go further, shall we?
How to prevent parasitoids and parasites from infecting your Monarchs
Just like with humans, cleanliness is key. For parasitoids like the Tachinid Flies, this is a bit more challenging. What I do is I try to keep an eye on my butterfly sanctuary (as much as humanly possible) and rid it of Tachinid Flies when I see them. All pupa are observed for any signs of Tachinid Fly parasitization (if you spot a dark or brownish spot on the green pupa during the two weeks, move that one to another location). If any silky, gelatinous strings 'fall' to the ground, destroy the pupa and the fly pupa that emerge.
With the Oe parasite I test ALL Monarchs that I raise before releasing them. If any show signs of the spores, I euthanize immediately.
I sanitize ALL equipment and rearing surfaces. This can help to keep bacterial and viral conditions to a minimum. I also try to make sure that the larvae are kept in as dry a condition as possible. High humidity leads to mold/bacterial/viral growth conditions so keeping all rearing conditions away from sun and heat is imperative. All containers are cleaned out at least twice if not more times a day. I do not put too many larvae in the same container either. Crowded conditions are not healthy in general.
The bottom line is: Be aware of what's going on with your Monarchs. If you do raise them, be smart and separate those that are not thriving so that they can be observed, and euthanize those that may transmit disease and illnesses.
What is a parasitoid? a parasite?
