Research Article

# Modelling a Historic Oil-Tank Fire Allows an Estimation of the Sensitivity of the Infrared Receptors in Pyrophilous Melanophila Beetles

• h.schmitz@uni-bonn.de

Affiliation: Institut für Zoologie der Universität Bonn, Bonn, Germany

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• Affiliation: Peter Grünberg Institut, Forschungszentrum Jülich GmbH, Jülich, Germany

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• Published: May 21, 2012
• DOI: 10.1371/journal.pone.0037627

### the sun as a factor

#### Posted by henricus on 17 Sep 2012 at 17:46 GMT

From their suspected starting points in the areas of Muir Grove and Kaweah River in California, the melanophila beetles had to fly the direction West-South-West (approx. bearing 240 to 260 degrees) to the burning oil tanks near Coalinga. That means, during their usual flight-time from 8:00 am to 8:00 pm they had to fly into the sun during the last hours of a flight day. From the 10th to 12th August, at 5:00 pm, the beetles had the sun head up, and at 8:00 pm the sun came approx. 20 to 30 degrees from the right (in relation to the flight direction).

In the middle of August, from 5:00 pm to 8:00 pm, the sun has an elevation angle between 30 to 10 degrees above the horizon. The radiation flux density of the sun in this case is approx. S0 = 1.367 W/m2 (“solar constant”) * sin [elevation angle] = 683 … 237 W/m2. The infrared part of this radiation energy has a percentage of approx. 46%. That means: during the last hours of their flight at a day the beetles “was looking” into the direction of the sun, an IR-radiation source with an infrared radiation flux density from approx. 100 to 300 W/m2.

My question: how it was possible for the beetles to find the burning oil tanks about a distance of approx. 80 miles by an IR-radiation flux density of 0,00007…0,0004 W/m2, in view of such a powerful infrared disturbance source like the sun in flight direction?

I put up six approaches for discussion:
1.) melanophila beetles are also flying after sunset in some cases
2.) the sun was not shining from the 10th to the 12th of August 1925, the weather conditions was characterized by dense blanket of clouds all the days >>> note: cause of the oil tank fire was a lightning strike in the morning 11:20 am, possibly during a thunderstorm; but in this case also the assumption of wind speed and groundspeed of the beetles should be reviewed
3.) the beetles which were found at the oil tanks came not from the western foothills of the extended forests of the Sierra Nevada (areas of Muir Grove and Kaweah River), but only from the San Benito Mountain area
4.) the IR receptors of the beetles are able to detect and to follow IR-radiation within a very small angle of beam spread
5.) the beetles are able to distinguish IR-Radiation of the sun from other IR sources
6.) there are still other factors of influence helping the beetles to find new reproduction areas as freshly burnt trees

Dipl.-Wirtsch.-Ing. Henry Pfeifer
Leipzig / Germany

fields of work:
- technical analytics
- bionics-inspired development

No competing interests declared.

### the sun as a factor / addendum 1

#### henricus replied to henricus on 19 Sep 2012 at 09:14 GMT

Hypothesis to assumption 5.)

The electromagnetic spectrum of sun radiation contains approx. 7% UV-radiation. The part of UV-radiation in the electromagnetic spectrum of a fire (candle, oil …) is near by Zero.

Possibly the melanophila beetles are also able to detect UV-radiation. By searching new reproduction areas then such targets are attractive for the beetles, which are emitting IR-radiation, but not UV-radiation. This could be an explanation why direct and indirect sunlight (reflection) is not a disturbance source.

Dipl.-Wirtsch.-Ing. Henry Pfeifer
Leipzig / Germany

fields of work:
- technical analytics
- bionics-inspired development

No competing interests declared.

### RE: the sun as a factor / addendum 1

#### helschmitz replied to henricus on 19 Sep 2012 at 13:58 GMT

This is an interesting aspect. However, up to now there is no evidence that Melanophila has UV vision capabilities. Many years ago we have ask Thomas Labhart from the University of Zuerich in Switzerland to look for a dorsal rim area in Melanophila acuminata. It clearly turned out that Melanophila does not have this specialized area in its compound eyes. For Review please refer to: T. Labhart and E.P. Meyer (1999) Detectors for polarized skylight in insects: a survey of ommatidial specializations in the dorsal rim area of the compound eye. Microsc. Res. Technique 47: 368-379.

Helmut Schmitz
Bonn University

No competing interests declared.

### the sun as a factor / the UV-hypothesis

#### henricus replied to helschmitz on 20 Sep 2012 at 23:54 GMT

The best way to learn more about known facts is to read a book with known facts. My preferred way to understand the secrets of nature is to do a step backwards, to get a view of the whole thing. Nature doesn't engineer needless things – that’s the only wall of mind I accept.

At

http://www.caesar.de/infr...

today I found a first description of the new technical IR-sensor, inspired by the sensor array of the melanophila beetle. The preamble of this website contains a figure 3 (“Abbildung 3”), which is showing a REM-close-up of such an IR-receptor of the beetles.

Beside of every IR-receptor (the globe-like stucture) there are to see a bit smaller structures with forms similar to a sweet pepper, and with up to 8…11 little holes. In the description of the REM-photo these holes are called "nano-pipes". A pipe-like structure is to see at the REM-photo in fact.

The scale in the REM-photo is shown with 10 µm. Compared with the scale the nano-pipes have diameters of approx. 250…400 nm (I only have appreciated, sorry). That means: these nano-pipes are closed for IR-radiation, but open for UV-radiation in the bands UV-A (close UV), UV-B (middle UV) and UV-C-FUV (fare UV). For these frequencies of UV-radiation the air is permeable (“transmissiv”).

I suspect, such a globe-like IR-receptor and these nano-pipes at it’s side must be considered as one unit.

The globe-like structure with a diameter of approx. 12-15 µm is able to detect parts of the mid-wavelength IR (MWIR) near 4 and 8 µm (IR-transmissvity-windows of the air in the MWIR), and parts of the long-wavelength IR (LWIR) from 8 to 11 µm, according to the diameter of the sensitive part of the “aperture” of the globe. How this detection works, is well researched already (the mikromechanic reaction, to read in the description at the referred URL at the beginning of this comment).

For the function of the nano-pipes I didn’t found a description yet. I suspect, the pipes contains receptors for a gas or gases which are development results if molecules of the air are reacting by influence of UV-radiation.

Furthermore, the pipe-like structure (a long hole) realizes a small angel of beam spread, see point 4.) of my first comment from the 17th Sep 2012.

A first attempt could be to search for O3-receptors. Ozone is not really a gas which is welcome in a organism – so the beetles would avoid flight directions with much UV-radiation automatically.

Dipl.-Wirtsch.-Ing. Henry Pfeifer
Leipzig / Germany

fields of work:
- technical analytics
- bionics-inspired development

No competing interests declared.

### RE: the sun as a factor / the UV-hypothesis

#### helschmitz replied to henricus on 23 Sep 2012 at 13:03 GMT

The pores next to the IR sensilla resembling tiny salt shakers are external openings of wax glands. Such openings (in lower numbers) accompany every (ordinary) hair-mechanoreceptor on the body of a Melanophila beetle. Please refer to:

A. Schmitz, A. Sehrbrock and H. Schmitz (2007) The analysis of the mechanosensory origin of the infrared sensilla in Melanophila acuminata (Coleoptera; Buprestidae) adduces new insight into the transduction mechanism.
Arthropod Structure & Development 36: 291-303

T. Vondran, K.-H. Apel and H.Schmitz (1995) The infrared receptor of Melanophila acuminata DE GEER (Coleoptera: Buprestidae): ultrastructural study of a unique insect thermoreceptor and its possible descent from a hair mechanoreceptor. Tissue & Cell 27 (6): 645-658

Helmut Schmitz

No competing interests declared.

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