I’m slowly making my way through all the photos I took this year, and I just finished August 6. That was the day of Julia’s family’s annual BioBlitz at Deep Woods Farm, their land in southeastern Ohio. A funny thing happened as Julia and I were heading back for dinner after the day’s exploration. We were walking past a little patch of monkeyflower (Phrymaceae: Mimulus ringens) that had popped up in an opening in the forest created when some trees blew down a few years ago…
…when something made me say, “if I were a fly, I’d mine the stems of monkeyflower.” There is no fly known to mine in the stems of monkeyflower (or in the leaves, for that matter), but just for the heck of it I stopped and took a look. It took only a moment to spot the first mine:
Since I was pretty sure this was something unknown to science, we of course had to delay dinner a little bit and spend a few minutes scouring the plants for larvae and pupae. We found several; here is the puparium of a larva that did its last bit of feeding in the midrib of a leaf:
At the far left end you can see its little black spiracular horns (breathing structures) poking out through the leaf epidermis. I’ll tell you more about these flies some other time, but the reason I’m bringing this up now is just to explain how we came to be closely examining monkeyflower stems, when Julia noticed that some of them were weakened toward the base. She broke one at its weak point and discovered a caterpillar inside:
The caterpillar had been busily converting the inside of the stem to mushy poop.
I figured that while we were collecting monkeyflower stems, we might as well see if we could rear this caterpillar.
The next day, the caterpillar had popped out of its stem, and it seemed uninterested in trying to enter another stem.
I had never tried to rear a stem-boring caterpillar before, but last summer when we visited MJ Hatfield in Iowa, she showed us how she was rearing all sorts of Papaipema (Noctuidae) caterpillars by offering them chunks of carrot to bore into. I wasn’t sure if this was a Papaipema, but I didn’t know what else to try, so I put it in a jar of soil with a carrot. It happily got to work turning the carrot to orange mush.
Weeks passed, and the carrot turned brown and shriveled down to the soil. When I put all my bugs into the fridge to overwinter at the beginning of November, there was no sign of an adult moth in the jar, and I was skeptical that the caterpillar had survived. Since I was running out of space in the fridge, I left that jar on a shelf in my office along with a few others that I considered to be lost causes.
When I came to the photos of the caterpillar just now, I decided to go and have a look in the jar, and when I unscrewed the lid this moth was waiting just below it, perched on a section of monkeyflower stem I had put in there along with the carrot:
I know next to nothing about noctuids, but I just browsed through the Papaipema pictures on BugGuide.net, and this seems like a good match for P. cataphracta, the so-called “burdock borer.” The guide page states that “larvae bore in rhizomes and stems of aster, burdock, corn, cottonwood, iris, lily, sunflower, thistle, tomato, and other plants.” So it sounds like this species will bore into just about anything with a stem. A couple of other species look pretty similar to this, but they are apparently specialists on the aster family; there are around 50 species in this genus, and my impression is that most of them are host-specific.
BugGuide also says that adults of Papaipema cataphracta fly from August to October, but there is one example of an adult that was found out and about in New Jersey on November 7 under natural conditions. I couldn’t say when in the past three weeks this monkeyflower one emerged; it’s perfectly alive, but it seems pretty sleepy and uninterested in flying at this point.