Wingless Wonderings

Over the winter I received a box of Nuttall oak acorns from Mississippi, containing cynipid wasp galls.  Over the past couple of days, several of these tiny (~1.5 mm) wasps have emerged:

The wings aren’t deformed; all of the wasps have dinky little wings like this, and they jump around rather than flying.  There are lots of adult wasps and other insects that have reduced wings or are missing them entirely, but this is only the second example I’ve seen in a chalcid wasp–the first being the Trichogramma alderfly egg parasitoids shown here (incidentally, I just updated that page with some corrections and new information provided by a Trichogrammatidae specialist, including the fact that both the winged and wingless individuals I photographed are females).  I suspected these were eulophids, and when I posted a couple of other photos of them on BugGuide, Ross Hill agreed, saying “The literature does mention brachypterous [reduced wings] or even apterous [wingless] members [of the family Eulophidae], although they are certainly not common.”

This prompted me to do a little search for said literature, and I quickly found several examples. Here* is the original description of Tetrastichomyia pulchricornis, apparently a caterpillar parasitoid; the wings are said to be “reduced to mere scale-like appendages which barely extend beyond the base of the abdomen.” No males had been found at the time of this description. Here** is the original description of Microdonophagus woodleyi, a parasitoid of Microdon larvae (these are really weird-looking syrphid fly larvae that live in ant nests). In this species, the females are fully winged and the males are brachypterous. And in this paper***, a species of Melittobia that parasitizes solitary bee and wasp larvae is reported to have three different female morphs: brachypterous “crawlers” that move away from light; fully-winged “fliers” that move toward light; and intermediate brachypterous “jumpers” that move toward light (like the wasps emerging from my box of acorns).  The proportions of these three morphs were experimentally shown to be dependent on the density experienced by the young larvae.

I’m only able to view the abstract of that last paper, but I’m guessing there were more winged individuals when density was higher, since wings are a handy mechanism for dispersal.  The question in my mind is, what’s the point of having reduced (or missing) wings to begin with?  Seems like most things would be glad to have a good set of functional wings, but having wings must be a liability in some cases.  I suppose the ability to fly increases the probability of being blown to unsuitable habitat.  A few times I’ve seen swarms of termites arrive at a new location and immediately shed all their wings.  Maybe ants do this too?  I’m not sure, but I’d be interested to hear other ideas about what’s going on with flightless insects.   I’ll leave you with a couple more examples of truly wingless wasps.

The one below is a 0.8-mm Trimorus (Platygastridae) I found last summer while sweeping the lawn with a glass, in search of tiny things to feed some spiderlings I was raising.

That wasp was very jumpy too, and also pretty cute, but this Baeus (another 0.8-mm platygastrid) photographed by Tom Murray takes the cake in that department:

I’ve been collecting examples of all the different wingless or brachypterous adult insects I can find here.

Added 6/21/2013: Christer Hansson has examined the eulophids from the acorns and determined that they belong to the genus Aprostocetus.

* Gahan, A. B. 1919. A new genus of chalcid wasp belonging to the family Eulophidae. Proceedings of the Entomological Society of Washington 21:2-4.

** Schauff, M. E. 1986. Microdonophagus, a new entedontine genus (Hymenoptera: Eulophidae) from Panama. Proceedings of the Entomological Society of Washington 88:167-173.

*** Freeman, B. E. and K. Ittyeipe. 2008. Morph determination in Melittobia, a eulophid wasp. Ecological Entomology 7(4):355-363.