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 mon ochromatic infrared radiation using a continuous wave CO overtone infrared laser. Best sensitivity was in the wavelength range 2.8-3.5 mu m. In this r ange a stimulus intensity of 14.7 mW cm(-2) was sufficient to generate sing le action potentials. At a wavelength of 5 mu m receptor performance signif icantly decreased. An increase in stimulus intensity caused a decrease in r esponse latency and an increase in the number of action potentials elicited . At a given wavelength (3.4 mu m) the dynamic amplitude range of action po tential 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 actio n potentials and a stimulus duration of 60 ms already caused response satur ation (with up to nine action potentials). In a repetitive stimulus regime distinct receptor potentials were visible up to a frequency of 600 Hz.