How can you tell if a pupa is alive or dead?

With most of our larvae turning dark brown and becoming much more still as they mature, it became quite difficult to tell the difference between a mature larva and a pupa. Really the only way to tell the difference is keep your eye on them for an extended period of time and look for movement- larvae move, and pupa do not.

But even more difficult to tell the difference between are pupa that are alive vs. pupa that are dead. As you can see from my last post, pupa are dark brown and shriveled and do not move whether they are alive or dead. I wanted to do a count of how many pupa we had that were still alive, so I took the 96 total pupa to Dr. A and asked her what to do.

Dr. A said that pupa respond to touch. So, you can place a pupa under a microscope and lightly touch it (for example, with the end of a small paint brush). If it is alive, it will wiggle for a second. If not, it will obviously remain still.

However, an interesting note is that when Dr. A and I performed the above procedure, absolutely none of the pupa responded to touch. But they didn't look dead either. Dr. A and I chatted for a few minutes and I happened to glance over at the container of pupa and almost all (~90%) were moving! I even had to ask Dr. A to confirm if they were moving for a moment because I thought I was going crazy. The most likely explanation for this is that these BSF were very mature larvae, on the verge of entering the pupa stage within about 24 hours.

In an attempt to keep this larva/pupa as happy as possible, I constructed a new container. On one side, I placed moistened coffee grounds and wet paper towels, and on the other, I placed dry bran with a slightly moistened paper towel on top. This would allow the mature larva to have their preferred conditions and feed until they reached the non-feeding pupal stage.