Sensitivity threshold and response characteristics of infrared detection in the beetle Melanophila acuminata (Coleoptera : Buprestidae)

The minimum detection threshold of the infrared sensitive beetle, Melanophi la acuminata, was measured with a helium-neon laser that emitted light at a wavelength of 3.39 mum. Extracellular recordings were taken both at the pi t organ responsible for detection and at the interganglionic connectives in the thorax of the beetle. At the pit organ, generator and action potential s from single neurons were measured with a sharpened tungsten electrode. At the connectives that linked the fused second meso-/metathoracic and protho racic ganglia, compound action potentials were measured with a tungsten hoo k electrode that encircled the connective. The latter recordings confirmed conveyance of infrared information through specific pathways to rostrally-s ituated sites in the nervous system of the beetle. The 50% probability irra diance threshold at which action potentials were elicited from the receptor and connectives occurred at 17.3 and 14.6 mW/cm(2), respectively, In addit ion to sensitivity threshold, several other characteristics of the response were quantified including dependence of generator potential latency, gener ator potential duration, spike frequency, and spike latency on irradiance, dependence of response strength (spike count) on exposure time, and flicker fusion frequency. The ability to detect infrared radiation is rare in natu re, and these results provide valuable information necessary to understand this unique sensitivity. (C) 2001 Elsevier Science Inc. All rights reserved .