Perception of Infrared Radiation by the Spiny Rat Mite Laelaps echidnina (Acari: Laelapidae)1

Abstract

Adult females of the spiny rat mite, Laelaps echidnina Berlese, were stimulated with incoherent infrared (IR) radiation. A response consisted of rapid, vertical movements or a single, laterally directed movement of legs I. In radiation tests with 1.6–7.0-wave lengths, the mites were most sensitive to a wavelength of 4.5 µ at an intensity of 0.25✕10−3 w cm−2. A test intensity (It), defined as the minimum intensity of radiation eliciting a 50% or greater kinetic response at the most sensitive wavelength, was established at 1.6✕10−4 w cm−2 and used at the 8 wavelengths subsequently tested. Responses above 50% occurred at wavelengths of 3.6 µ(60%), 4.5 µ (74%), and 5.0;µ(51%); responses below 50% were at wavelengths of 4.3 µ (26%), 6.0 µ (30%), and 7.0 µ (23%). Less than 3% response occurred at wavelengths of 1.6 and 2.2 µ. It was demonstrated that when tarsi I were positioned out of the beam or were amputated, the percent response of individuals, at the most sensitive wavelength (4.5 µ) at It, decreased to 3% and 8%, respectively. The IR receptors for those wavelengths tested appear to be located primarily on tarsus I. It is proposed that the IR receptors are the thin-walled setae on tarsus I and that they function as dielectric IR waveguides. This proposal is supported by the comparison of expected structural characteristics, such as base diameter, length, and taper, of an optimally designed dielectric antenna with the observed characteristics of the thinwalled setae on tarsus I.