Die Rolle von Infrarotstrahlung bei der Flugsteuerung von pyrophilen australischen Insekten
Zusammenfassung der Projektergebnisse
Infrared (IR) receptors are rare in insects and have only been found in the small group of so-called pyrophilous insects, which approach forest fires. In previous work the morphology of the IR receptors and the physiology of the inherent sensory cells have been investigated. It was shown that receptors are located on the thorax and the abdomen respectively and show an astounding diversity with respect to structure and the presumed transduction mechanism. What was completely missing, however, was any behavioral evidence for the function of the IR receptors in pyrophilous insects. In the completed project we investigated the responses of the Australian “firebeetle”, Merimna atrata to IR radiation. Beetles in a restrained flight were laterally stimulated with IR radiation of an intensity 20% above a previously determined electrophysiological threshold of the IR organs (i. e. 40 mW/cm²). After exposure, beetles always showed an avoidance response away from the IR source. Reversible ablation experiments showed that the abdominal IR receptors are essential for the observed behavior. Tests with weaker IR radiation (11.4 mW/cm²) also induced avoidance reactions in some beetles pointing to a lower threshold. In contrast, beetles were never attracted by the IR source; even if weak IR radiation with an intensity of less than 1 mW/cm² was tested. Our results suggest that the IR receptors in Merimna atrata serve as an early warning system preventing an accidental landing on a hot surface. We also tested if another fire specific stimulus, the view of a large smoke plume, influenced the flight. However, due to an unexpected insensitivity of the flying beetles to most visual stimuli results were ambiguous. The marked insensitivity to visible light (and many other kinds of optical stimuli) was a rather unexpected finding. Even if we suddenly radiated intense bright white light from one direction onto the flying beetle no change in flight direction could be observed. This is in striking contrast to observations in the field, where escape distances of several meters are common if e. g. a human approaches a beetle resting on a tree. The visual insensitivity of beetles in a restrained flight may be the reason for the inefficacy of the sight of a smoke plume. The reasons for this behavior remain enigmatic.
Projektbezogene Publikationen (Auswahl)
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(2018). The impact of infrared radiation in flight control in the Australian “firebeetle” Merimna atrata. PLoS ONE, 13(2), e0192865
Hinz, M., Klein, A., Schmitz, A., & Schmitz, H.
