Responses of the infrared sensilla of Melanophila acuminata (Coleoptera: Buprestidae) to monochromatic infrared stimulation.

The pit organs of the beetle Melanophila acuminata were stimulated with monochromatic infrared radiation using a continuous wave CO overtone infrared laser. Best sensitivity was in the wavelength range 2.8-3.5 micron. In this range a stimulus intensity of 14.7 mW cm(-2) was sufficient to generate single action potentials. At a wavelength of 5 microm receptor performance significantly decreased. An increase in stimulus intensity caused a decrease in response latency and an increase in the number of action potentials elicited. At a given wavelength (3.4 microm) the dynamic amplitude range of action potential responses covered 12 dB. At high stimulus intensities (94.2 mW cm(-2)) a stimulus duration of 4 ms was sufficient to generate one to two action potentials and a stimulus duration of 60 ms already caused response saturation (with up to nine action potentials). In a repetitive stimulus regime distinct receptor potentials were visible up to a frequency of 600 Hz.