Light trap

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Light trap "Walz" 12 V, 8 W, (" black light ")
Many insects are attracted by light sources.
Spectral decomposition of solar radiation : Sunlight has a continuous spectrum.
Sensitivity distribution of human photoreceptors in rods (dashed in black) and the three types of cones (S, M and L).

A light trap is an apparatus for catching night-flying insects with the help of a light source.

Mode of action

Light traps attract insects with a high proportion of blue light and / or ultraviolet radiation . The most attractive spectral ranges for moths are at wavelengths between 350 and 550 nanometers (with particular effectiveness around 420 nanometers), i.e. especially in areas that are partially invisible to humans. Pure ultraviolet lamps also have an attractive effect, while lamps without an emission component in the ultraviolet spectral component show only weak attraction, although it has been proven beyond doubt that the insects can see this light.

The reason for the attraction is not fully understood. Various hypotheses have been put forward to explain this, none of which has yet been able to explain the phenomenon in all its manifestations satisfactorily.

  • Compass hypothesis: One hypothesis is that insects orient themselves to the light from celestial bodies. Since celestial bodies are so far away that their light appears as a directional (i.e. parallel) light source, the angle of incidence to the earth remains the same over long times or distances. However, nearby light sources (like light traps) emit the light from one point. Insects try to correct the mistakenly detected wrong direction and change their angle to the light source. Since natural light does not normally come exactly from above, the angle is not exactly 90 °. This drives them into a spiral, and ultimately into the trap. A corresponding movement pattern has been demonstrated in a butterfly species, the housemother ( Noctua pronuba ). Most species do not approach the light source in a corresponding spiral path, but fly towards it in a straight line or show other movement patterns.
  • Glare hypothesis: According to another hypothesis, the artificial light source disrupts the natural orientation mechanisms of the species. These lose their orientation, which means that they are no longer able to leave the area of ​​influence of the light source. Many types such as B. Swarmers do not fly directly into the light source, but rather sit down at some distance from it. Others such as the cotton boll borer ( Heliothis zea ) fly in a circular path at a defined distance from the light source, on which they land directly at most from exhaustion. The nocturnal orientation is possibly based on a finely balanced structure of different sensory stimuli, which are unbalanced by the strength of the artificial light source. Just like the human eye, the insect's eye also has a dark adaptation that is lost through glaring light.
  • Polarization hypothesis: In contrast to the human eye, most insects can see the plane of oscillation of polarized light. The majority of them are based on the polarization pattern of the sky to determine the position of the sun or moon when the sky is overcast, to find water surfaces, for intra-species communication and to find flowers that offer special polarization patterns. The reflection of polarized light was an almost unmistakable sign of water surfaces until the arrival of humans. Since most light traps also emit polarized light, they could act as an overly strong distraction stimulus. Many species attracted by light traps live in or around water.

Other hypotheses exist in large numbers. It is suggested, among other things, that many species are adapted to fly to bright clearings in the forest for which the light trap offers an over-optimal substitute stimulus. Others have suspected that the sudden bright light is misinterpreted as daylight by the nocturnal species, so they sit down to hide. It is not unlikely that there is no single explanation that applies to all species.

Catch radius and influencing factors

The radius in which a light trap will attract is difficult to predict in general and depends on numerous factors. In control tests under scientifically controlled boundary conditions, capture radii between 3 and 150 meters were determined. Typically, the catching radius of butterflies is rather limited and only exceeds 10 to 15 meters in exceptional cases. In an investigation in which, in addition to the light traps, the actual colonization of the adjacent biotopes (by catching and identifying the caterpillars) was determined, populations that developed at a distance of 10 meters from the light trap (a common standard model) were no longer lured. In particular, aquatic insects such as mayflies or caddis flies are sometimes attracted over many hundred meters. Known influencing factors on the catchability include: a .: Weather (better catches with warmth and high humidity), ambient light (better catches with new moon and with little additional light sources in the vicinity), time (different depending on the species and region, sometimes in the early hours of the night, sometimes . Peak at midnight). It is also known that males are more attracted than females.

purpose

Light traps are used for both scientific and commercial purposes. The former includes research into the behavior and distribution of nocturnal insects, especially moths . The determination of the distribution area is hardly possible statistically with a single light trap; however, this can be used to record the individual species. With several traps, if their spatial distribution is known, the quantitative occurrence of insects and their habitat attachment (attachment to a habitat) can be determined. Light traps are also used to catch live; for this they have to be emptied at short intervals.

In private homes and in bakeries, for example, mosquito and wasp killers are used, which, in addition to a light source, often contain a high-voltage grid or a fan to kill the insects. Alternatively, attractant traps catch insects using special scents.

criticism

The use of light traps has been criticized by nature conservation organizations , as these traps can also endanger rare insects.

With regard to the detection of species, the selective attractiveness of the traps must be taken into account - the light traps do not attack different species with the same intensity.

literature

  • Michael Mühlenberg: Outdoor Ecology. (3rd, revised edition.) UTB , 1993, ISBN 3-8252-0595-9 , p. 414.
  • Kenneth D. Frank: Impact of outdoor lighting on moths: An assessment. In: Journal of the Lepidopterists Society. Volume 42, No. 2. 1998, pp. 63-93.
  • Kenneth D. Frank: Effects of artificial night lighting on moths. In: Catherine Rich, Travis Longcore: Ecological Consequences of Artificial Night Lighting. Island Press, 2005, ISBN 1-55963-129-5 .

Web links

Commons : Light Trap  - Collection of images, videos and audio files

Individual evidence

  1. ^ Claude Dufay: Contribution à l'étude du phototropisme des Lépidoptères noctuides. In: Annales des Sc. Nat. Zoology. Series 12. T. IV., Paris 1964.
  2. ↑ Karl Cleve: The spectral perception of butterflies flying at night (Lep.). In: Bavarian Entomologists' newsletter. 16th year 1967, No. 5/6.
  3. ^ Günter Ebert (Ed.): The butterflies of Baden-Württemberg. Volume 3: Moth I - root borer (Hepialidae), wood borer (Cossidae), ram (Zygaenidae), snail moth (Limacodidae), sack bearer (Psychidae), window spot (Thyrididae) Ulmer Verlag, Stuttgart 1993, ISBN 3-8001-3472-1 .
  4. ↑ Karl Cleve: The starlight and its presumed perception by butterflies flying at night. In: German Entomological Journal. New episode Volume 13, Issue IV / V, born in 1966.
  5. ↑ S. Sotthibandhu, RR Baker: Celestial orientation by the large yellow underwingmoth. Noctua pronuba L. In: Animal Behavior. Volume 27, Part 3. 1979. pp. 786-800.
  6. ↑ Jan Beck, K. Eduard Linsenmair: Feasibility of light-trapping in community research on moths: Attraction radius of light, completeness of samples, nightly flight times and seasonality of Southeast-Asian hawkmoths (Lepidoptera: Sphingidae). In: Journal of Research on the Lepidoptera. 39. 2006. pp. 18-37.
  7. ↑ HS Hsiao: Flight paths of night-flying moths to light. In: Journal of Insect Physiology. Volume 19, No. 10. 1971-1976 (1973).
  8. ↑ Gábor Horváth, György Kriska, Péter Malik, Bruce Robertson: Polarized light pollution: a new kind of ecological photopollution. In: Frontiers in Ecology and the Environment . 7. pp. 317-325. (2009).
  9. ↑ Alison Sweeney, Christopher Jiggins, Sönke Johnsen: Brief communication: Polarized light as a butterfly mating signal . In: Nature . No. 423, May 1, 2003, pp. 31-32. Retrieved March 17, 2013.
  10. ↑ Gábor Horváth, et al .: Does reflection polarization by plants influence color perception in insects? Polarimetric measurements applied to a polarization-sensitive model retina of Papilio butterflies . In: Experimental Biology . 205, Nov. 1, 2002, pp. 3281-3298. Retrieved March 7, 2013.
  11. ↑ Ludger Wirooks: On the surface reference of light- catching species spectra (Lepidoptera, Macroheterocera). In: Communications of the German Society for General and Applied Entomology. 15. pp. 403-408. (2006).
  12. ↑ Travis Long Core, Catherine Rich: Ecological light pollution. In: Frontiers in Ecology and the Environment . 2. pp. 191-198.
  13. ↑ Florian Altermatt, Adrian Baumeyer, Dieter Ebert: Experimental evidence for male biased flight-to-light behavior in two moth species. In: Entomologia Experimentalis et Applicata. Pp. 130: 259-265. (2009).