Tuesday, May 14, 2013

The hidden world of the crouching tiger-beetles

An ultrasound detector
Tiger beetles are an iconic group for many entomologists and ecologists. They have been considered to be a good surrogate group for use in biodiversity studies. They are perhaps not as good as the more ecologically dominant ants, but are certainly full of character and action. To add to that, most of them can be found on open paths, saving the need to dash through vegetation and load oneself with ticks. Unfortunately, nobody has quite made an illustrated fieldguide for the Indian region despite the ease of making one especially for someone with access to a good collection. Perhaps the museums have not been welcoming to anyone who might be motivated. A major reference for the Indian region is by R. Acciavatti and David Pearson (Acciavatti, R.E.; Pearson, D.L. 1989: The tiger beetle genus Cicindela (Coleoptera, Insecta) from the Indian subcontinent. Annals of Carnegie Museum, 58). 


C. venus up front
A somewhat less studied aspect of tiger beetles is the production and hearing of ultrasound. Some years ago I went out on a bat-watching outing with the Norwegian Zoological Society to a lake to the east of Oslo. Equipped with bat-detectors, we were able to hear more bats than we could see. It is simply fascinating when a world that our senses do not detect is suddenly made perceptible. I think this is the fundamental allure of photography (showing detail we may not spot), microscopes, binoculars, ultrasound detectors, DNA sequencers and a most other instrumentation. Anyway, I would love to hold a sensitive bat-detector up close to these critters.


Cicindelids apparently hear ultrasound using two "ears" on the dorsal side of the first abdominal segment. They respond to bat pulses with escape behaviour and also produce ultrasound at around 30–35 kHz in non-defensive contexts, perhaps for communication. According to one study the production of ultrasound in flight is possibly through a mechanism that involves the elytra and wings. I however wonder if they may be producing other sounds through mandibular stridulation, when not flying. They often seem to gnash their jaws, mandibles crossing over each other and perhaps the micro-structure of the flat mandibular surface will have something to reveal. Someday hopefully we can hear these beetles, who knows they might even be detected and identified by their sounds.

A regular on forest paths in the Western Ghats
Cicindela (Cosmodela) duponti Dejean, 1826
Another view of
Cicindela (Cosmodela) duponti Dejean, 1826


Cicindela (Jansenia) venus Horn, 1907
another forest species found on leaf-litter
Cicindela (Calochroa) hamiltoniana Thomson, 1857
most times seen on shaded paths close to water
Cicindela aurofasciata Dejean, 1831
a stouter species found on open grassy habitats
Cicindela (Calochroa) flavomaculataHope, 1831
One of the few species more often attracted to light in the night

Lophyra lineifrons, Bandipur (April-2013) [Determined by Michael Geiser]
Cicindela (Calochroa) whithilli (Hope) from Talakaveri, Coorg
Cicindela (Ancylia) calligramma Schaum, 1861 from near Nandi Hills, Bangalore (15-July-2013)


To be determined. Mudigere, 11- May 2013
Cylindera (Eugrapha) sp. Seen in large numbers on sand beside stream (11-May-2013).
(Identified to genus by Michael Geiser - 5-Dec-2013)
Cicindela (Jansenia) dasiodes Acciavati & Pearson, 1989 (from GKVK, 19-June-2013)

A feature that makes tiger beetles particularly interesting for those interested in electronic field guides is their patterning. It would appear as if there was a fairly simple archetypal "bodyplan" (what the Germans called Bauplan, but often avoided because of an implicit idea of "design"). An archetypal plan is however possible without any fear of "intelligent design" if one considers that patterns are coded by sections of genetic code, modules of which are shuffled about during the evolution of species. An amazingly old (1917) work on this is by Shelford and he identifies patterns of colour and provides some interesting insights into developmental biology. By subjecting larvae and pupae to specific environmental conditions of temperature and humidity he was able to alter the patterns that form on the elytra of the adults.


"Showing the geographic distribution of types and patterns. The first series at the left are world-wide in distribution, being most generalized in Eurasia and North America. The second group of patterns belong to several groups of species but all are characterized by the presence of three spots at the base and along the elytral suture. They are most numerous in Africa and India. The next group shows the relatively rare type with the pattern oblique but in the opposite direction from the slope of the tip of the elytron. The last type is one showing peculiar joinings of markings characteristic of species found chiefly in • Indo-Australian region." (Shelford, 1917)

Inspired by Shelford, I attempted to look at the patterns on some Indian species. It is however very difficult to see much without access to museums or other collections.

Patterns on a handful of Indian species - easily drawn using Inkscape

 
Acknowledgement

Most of the photos were taken on field trips either accompanied or made possible by Dr. Revanna S. Revannavar, entomologist at the University of Horticultural Sciences, Mudigere.
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References

Postscript
Would be terrific if someone can come up with a low-cost ultrasound monitoring instrumentation in India - based on ideas such as this. Would be very happy to help in field testing for any electronic whizzes out there that might be interested.


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