Introducing Longhorned Milkweed Beetle Larvae to The Milkweed Plants – Blog Post 5

The beetle eggs have started hatching (again)! Instead of transferring the long grass stems from the beetle habitats to the kiddy pool, I added the stems to an incubation chamber in the greenhouse. I had hoped to use the roots of the kiddy pool plants as food for the larvae so that they could grow a little bit bigger before I introduced them to our experimental plants. Due to the time constraints of the summer research session, I am introducing this second set of larvae directly to the experimental plants and allowing them to feed for eleven days. These are the experimental treatments: Control – no larvae, Low – 2 larvae, Moderate – 4 larvae, and High – 8 larvae.

After doing some research last week, I discovered a possible explanation for the missing larvae in the kiddy pool. I thought that the larvae fed on the fine roots, but I read a few articles stating that the larvae may actually burrow inside the coarse roots and feed on them. I tested this idea by introducing the two larvae found in the kiddy pool to an experimental plant and allowing them to feed. I harvested the pot yesterday and was really excited to find one of the larvae feeding on the inside of a coarse root! I could see a distinct difference between the healthy coarse root tissue and the coarse root tissue damaged by the larvae. Based on this discovery, I will dissect the coarse roots at the end of the eleven-day feeding period to look for larvae. I still do not feel like I know enough about the feeding habits of the larvae, so I hope to run a small experiment this week to see if I can observe more of them feeding on the roots.


A larva inside a coarse root


  1. Courtney Alston says:

    Your study sounds fascinating! Since I am such a squeamish person, I could never work with larvae. How do you feel working with bugs?

  2. dmyagmarsuren says:

    I’m glad that your second round of eggs started hatching! It’s interesting that the larvae might be “hiding” in the coarse roots. How big are the coarse roots? Do you think they’re big enough to keep most of your larvae?

  3. lanajagannathan says:

    It was super interesting to read about the larvae and their interaction with the Milkweed roots. I would have never guessed that they could burrow inside the roots! I also loved reading about the process you took to arrive at that conclusion—using what you learned from the literature in combination with a short side-experiment. This reminds me of my own research/problem solving process, since I’ve had to read plenty of articles and revise procedures based on smaller side experiments when things didn’t work out. Looking forward to reading about how your experiment turns out!

  4. mrdonnan says:

    I love working with bugs! I grew up playing in the soil and picking up insects all the time, so I think that’s part of why I have no problem working with the larvae. The longhorned milkweed beetle is particularly adorable (see blog post 1 for a photo).

  5. mrdonnan says:

    The coarse roots of the experimental plants have ranged between 2.5 mm and 3.5 mm in diameter so far, so they are definitely big enough to house the larvae, which are smaller than the tip of my fingernail after the eleven-day feeding period. I did not measure the diameters of the plants in the kiddy pool, but the aboveground growth of the plants was smaller than the experimental plants, so I bet the diameters of the coarse roots would have been smaller as well.

  6. mrdonnan says:

    Thanks so much!