Behavioral analysis of light intensity discrimination and spectral sensitivity in the honey bee, Apis mellifera

Abstract

1. The spontaneous choice behavior of bees between two lights—a reference light of constant intensity (I_c) and a test light of variable intensity (I_v)—was tested by means of a binary choice apparatus. 2. The intensity discrimination threshold for white light was determined in an intensity range of five powers of ten. Defining 65% choice frequency as reaction threshold, an intensity difference of 14.5% is perceived at the highest intensity tested (I_c = 3.6 W/m² = relative intensity 1). This difference increases only slightly, to 18.7%, with a decrease in relative intensity to 10⁻³, but at a relative intensity of 10⁻⁴ it increases to 57.2% (Fig. 3). 3. According to these findings the least potential difference noted at receptor niveau is about 1 mV as can be determined by means of the intensity characteristic of the photoreceptors (Fig. 8). 4. The intensity discrimination sensitivity in ultraviolet, blue, and green monochromatic light was determined. No significant differences were found (Fig. 4). 5. An action spectrum, i.e., the spectral sensitivity function of the spontaneous phototactic choice behavior was determined by measuring the intensities of different monochromatic lights which are equally attractive as the constant reference light (I_c). It has maxima in the ultraviolet (350–360 nm) and in the green range (530–540 nm; Fig. 5). The relative amplitude of the maxima depends on the intensity of the reference light: The green sensitivity decreases when the intensity of the reference light is increased (Fig. 7, insert).

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