Parasitoids are insects that live in or on the body of a single host individual, eventually killing it. They live in their host as larvae and sometimes pupae, but the adult parasitoids are almost always free-living. So, for example, a parasitoid fly lays eggs on a caterpillar, the fly egg hatches into a larva that burrows into the caterpillar, and the fly larva lives and grows inside the caterpillar. When the fly larva is done growing it burrows out of the caterpillar, pupates, and becomes an adult. The host caterpillar dies just before the fly larva burrows out of it because the fly has eaten so much of its body.
Two things make parasitoids hard to study. First, because the adults don't live in their hosts, entomologists often catch the adults and have no idea what their host species are. Second, in order to figure out host/parasitoid interactions, we need to catch the susceptible host stages in the wild where they've been exposed to potential parasitoids, bring them inside, raise them on their proper host plants, and see what comes out of them. That's a lot of work.
Over the past 13 years, MLMP volunteers have collected over 10,000 monarch caterpillars to help us learn more about monarch parasitoids. We've learned about when monarchs are most vulnerable to parasitoids, and that one particular parasitoid fly, called Lespesia archippivora (it doesn't even have a common name!) is the most important monarch parasitoid all over the U.S. We've also learned that a tiny wasp, called Pteromalus puparum (it doesn't have a common name either) attacks monarch pupae. Before citizen scientists did all of this work, we didn't know much at all about monarch parasitoids.
Why is this important? Natural enemies--like predators, parasites, and parasitoids--are responsible for most of the mortality suffered by insects. If we understand these natural enemies better, we can better understand how to protect insects, like monarchs, from human-caused mortality.
Wanted dead or alive: Monarch parasitoids
Collect 4th and 5th instar monarchs from your MLMP site or any stage of monarchs from other sites, and record the stage at which you collected them and whether the monarchs produce parasitoids (wasps or flies, and how many wasps or flies), adult monarchs (males or females), or die of some unknown cause. Enter your data under activity 3 at www.mlmp.org. Even better, package any parasitoids you get, and send them to the University of Minnesota for identification. For more detail, see the MLMP activity 3 data sheet.
University of Minnesota Monarch Lab
- A tachinid fly larva (or maggot) emerging from a monarch pupa. Photo by MLMP volunteer Stephanie Baker.
- A tachinid fly adult. Monarch Lab photo.