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Index of Subjects Hi Nancy: Each of the six legs of most insects investigated carries a sensitive mechanoreceptor organ in the tibia, just below the 'knee', aptly called the sub-genual organ (SGO). It contains ~25 chordotonal sense cells (mentioned earlier re insect 'ears') strung around a membrane that spans a blood channel in the leg, a bit like a stretched trampoline. It's primarily a ground vibration detector. In cockroaches, the leg's displacement threshold to elicit a response is about the same as that in the basilar membrane at the threshold of hearing in the cochlea, ~1 nanometer, so it's exquisitely sensitive. A German scientist that I'd met briefly earlier had observed pelecinids while vacationing in Canada a few years ago. He wrote suggesting that the extremely enlarged tibia of the hind legs, clearly visible in your photo, might contain a mega-SGO, that might be what the wasp used to detect vibrations emanating from June beetle larvae underground. This could be worth investigating and he was interested to do so. So I collected a couple of the wasps (apparently not available in Germany), and painstakingly fixed and embedded the swollen tibiae for electron-microscopy and sent the blocks to him to cut sections and examine, since that's what he seemed to want to do. I later learned from a junior colleague there that he had given up doing things himself and had become a lab manager-bureaucrat, so the blocks were sitting on his shelf and the project never went any further. In fact he probably really wanted me to do it so that we could 'collaborate' (X actually does the work while Y gains partial credit, the way of the science world these days). If this project had gone forward, it still would not have solved how the wasp decides to land on which bit of the lawn to check for vibrations. It would be interesting to see if the pelicinid SGO responds also to airborne sound, as does the cockroach SGO, though it is hard to imagine how much airborne sound could be generated from a beetle larva scrunching around inches underground (you'd have to measure it at different frequencies). The adults typically are out flying about now, late August, often cruising over lawns. As has come up before on NatureNS, there is just the single N. American species, and those seen are always females. Males are known but are much smaller and are never usually found -- reproduction may be mostly without male intervention. Steve (Halifax) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Quoting nancy dowd <nancypdowd@gmail.com>: > There have been some fascinating posts lately about some of our > parasitic (and hyperparasitic) wasps. Here is another one that seems > to be everywhere right now- a Pelecinid (Pelecinus polyturator): > > http://www.flickr.com/photos/92981528@N08/9612734497/ > > Another, more ominous looking, using the flash: > http://www.flickr.com/photos/92981528@N08/9616020630/ > > They are big (40mm as shown) and hard to miss. > > Somehow (sound/vibration?) mother Pelecinid detects larvae below > ground, jabs her abdomen in the soil and lays a single egg on one, > often a June Beetle grub from what I read. > > Nancy
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