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| Teleopsis The strawberries at the ends of the handle-bar are the eyes. |
It was not too long ago that I first learnt about an insect with eyes on stalks. Somehow, nobody had introduced it in our student days and for us (true) stalked eyes were found only in the crustacea. When I first came across it and discovered that it was hardly uncommon, it was a bit depressing to see that there were no experts who could identify it to species. Apparently problems had been created in the museums with labelling errors. I had uploaded my photographs on Wikimedia Commons and only recently obtained a species level identification of it - actually a confirmation of my own part-guess based on old literature - Teleopsis sykesii (named after Colonel Sykes). A redescription of the species that makes use of photographs of yours truly as well as the superior images of Karthik has just been published.
- H. R. Feijen, C. Feijen (2011) On the biogeographic range of the genus Teleopsis Rondani (Diptera: Diopsidae), with redescription of Teleopsis sykesii from India and description of a new species from Borneo. Zoologische Mededelingen, 85:141-159. (PDF)
It is interesting that this these are not the only flies with elongated eye bases - apart from the Diopsidae, the feature is also seen in the Richardidae. A very interesting piece of footage in one of Sir David Attenborough's Challenges of Life - shows how the fly emerges from the pupa looking more or less like a typical fly and then inflates the tubular stalks with air to form the elongated eye stalks. In most other insects, this kind of expansion of structures is done by pumping liquids that then subsequently dry - as in the case of the Lepidoptera. The use of pneumatic (perhaps aerostatic is the equalent of hydrostatic) structural elements seems to be rather rare in life - indeed I have not been able to find any other. Strangely enough however, there are a number of ideas in robotics (including the art of Theo Jansen) and tent making that use pneumatically operated structures, after all it means you use the air around you and save yourself from carrying extra construction baggage.
- Buschbeck EK; JL Roosevelt & RR Hoy (2001) Eye Stalks or No Eye Stalks: A Structural Comparison of Pupal Development in the Stalk-Eyed Fly Cyrtodiopsis and in Drosophila. The Journal of Comparative Neurology 433:486 – 498 (more on inflation of eyes)
Actually, insects use air to inflate their bodies all the time. Every molt is accompanied by air-swallowing that allows the enlargement of the new cuticle. Also, air-swallowing is used to increase fluid pressure so that hemolymph can be moved around in insect bodies, within which large cavernous spaces called "air sacs" can often be found, from beetles to dragonflies. I would not say that Buschbeck et al.'s (2001) explanation of air filling the eye stalks is very binding. First, it is suspicious that air should be pumped at the same speed as hemolymph, though the wings are certainly primarily receiving the latter (yet both the wings and eye stalks are expanded "simultaneously"). Second, hemolymph is remarkably clear: look at the wings themselves. Third, the wings receive both air and hemolymph, so cutting a wing could stop the flow of either. (It is conceivable that the hemolymph clogs, so it would not drip out of the tip of the wing.) The insect circulatory system is open; however, the tracheae are not continuous. That is, the tracheae branch off and supply different portions of the body with oxygenated air; otherwise, were you to cut the wing, you would expect a large portion of the insect to asphyxiate. All these things suggest that it is hemolymph that actually expands the eye stalks. Whatever the case, there is certainly going to have to be hemolymph coursing through the eye stalk to supply the optic nerve and the rest of the eye with nourishment and to remove wastes. However, even if the eye stalks were initially filled with air, they would not be pneumatic. That is, you couldn't poke a hole in an eye stalk and watch it deflate. That's because after initial expansion, the appendage would sclerotize and harden, like the legs, antennae, etc., of this and other insects. The eye stalks would still contain air within them (the eye will need to be supplied with oxygen), but they would not be pneumatic.
ReplyDeleteInteresting comments. Would you have references on the use of air in insect moulting? I presume that by "swallowing" you are referring to the bellow like actions of the abdomen at the spiracles... swallowing via the mouth would be rather surprising...
ReplyDeleteNo, I am referring to actual swallowing (and sometimes of water, if that's where the larvae or pupae are living). An insect can't provide enough pressure from air taken in by the spiracles, even by means of active ventilation, and at any rate, the insect still needs to breathe.
ReplyDeleteI mostly concentrate on wing expansion (i.e., adult ecdysis / eclosion), so I have more references to those papers. But try: Frederick Knab, 1909, "The role of air in the ecdysis of insects"; Cottrell, 1964: "Insect ecdysis with particular emphasis on cuticular hardening and darkening."; and/or Ayali, 2009: "The role of the arthropod stomatogastric nervous system in moulting behaviour and ecdysis".
For the role of air-swallowing and wing expansion in eclosion and post-adult ecdysis see, for example: White and Ewer, 2014: "Neural and hormonal control of postecdysial behaviors in insects"; Miles and Booker, 1998: "The role of the frontal ganglion in the feeding and eclosion behavior of the moth Manduca sexta"; Fraenkel, 1935: "Observations and experiments on the blow-fly (Calliphora erythrocephala) during the first day after emergence".
BTW, when I referred to clear hemolymph, this is best exemplified during wing expansion, when hemolymph expands the wings by being 'injected' between their dorsal and ventral surfaces.
Very interesting, thanks for the references!
DeleteYou're welcome. I'm glad you're enjoying them!
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