Well, I’ve just finished the fifth of the ten reports I have to submit by the end of the year, so I suppose I can afford to pause for a moment and fill you in on some breaking news in the world of gall midges.
When Julia and I arrived in the Chihuahuan Desert one evening three and a half weeks ago, we discovered that it had rained a few weeks earlier, following a long drought, and all sorts of wildflowers were blooming as a result. There was a lot of ocotilllo (Fouquieria splendens) around, but these scraggly plants didn’t seem to be participating in the flower show, until I spotted a single plant with four flowering spikes:
I bent down one of the thorny stems to have a closer look…
…and a tiny mosquito-like fly caught my eye. It had dark-tinted wings and an orange body. “Hey, is that a gall midge?” I wondered. It flew away before I could attempt a photo, but then Julia noticed that almost every flower bud had something sticking out of it:
I recognized these as pupal skins of gall midges; we had apparently just seen one of the last ones to emerge. Only a few of the flowers on the plant had managed to open all the way, and the rest had all aborted because of the larva of one of these midges feeding inside. Knowing how incomplete our knowledge is of inconspicuous little bugs in the desert, I figured there was a reasonable chance that no one had found these before, so I scoured the flowering spikes for buds that did not yet have pupal skins sticking out of them, and filled a vial or two.
Two days later, I noticed similar pupal skins poking out of unopened flower buds of narrowleaf globemallow (Sphaeralcea angustifolia).
In this case, try as I might, I couldn’t find any buds that seemed likely still to have anyone inside them, but I collected a few of the buds with pupal skins in case something could be determined from these. That evening when we returned to camp, I discovered that one of the ocotillo midges had emerged.
I had accumulated several more adults by the time I got home, and when I checked Gagné (1989)*, I confirmed my suspicion that neither the ocotillo nor the globemallow midges had been recorded before. I sent my specimens to Dr. Gagné–who could tell from my photos that both were Asphondylia species–and this morning he reported back:
The Asphondylia pupa with the Sphaeralcea looks like something unique, but those with the Fouquieria look a lot like A. websteri Felt. I couldn’t say for sure, though, whether the latter is websteri unless I had larvae also, but I suspect it is.
So, the globemallow midge is likely an undescribed species, but it will have to remain nameless until someone comes up with some larvae and adults. I looked up Asphondylia websteri and learned that it has been found from California to Oklahoma, south to Mexico, and it has been reared from deformed pods of alfalfa (Medicago sativa) and guar (Cyamopsis tetragonoloba), as well as aborted flowers of native legumes in the genus Parkinsonia, plus aborted fruits of jojoba (Simmondsia). I asked Dr. Gagné if he knew of any additional hosts, and remarked that it seemed odd for a gall midge to feed in plants of three different orders. His reply:
Yes, A. websteri is now found also on avocado and green beans in Mexico. It’s just a bud-feeder, unlike lots of other species that make complex galls and have a more long-term connection to their hosts. We also know now of some Old World Asphondylia generalists and of some species that have alternate hosts on different plant families.
So there you have it. I did wonder what the heck those emerging midges planned to do if there wouldn’t be any more ocotillo flower buds to lay eggs in for months. If pretty much any flower bud will do, finding the next host becomes a much less difficult task.
* Gagné, Raymond J. 1989. The Plant-feeding Gall Midges of North America. Ithaca, NY: Comstock Publishing Associates. 356 pp.