Behavioral experiments on the visual processing of color stimuli inPieris brassicae L. (Lepidoptera)

Summary In spontaneous-choice experiments on the butterflyPieris brassicae L. (Pieridae), spectral-effectiveness and spectral-sensitivity functions were obtained for various behaviors.Pilot experiments with colored PVC films, for which the relative number of reflected quanta with regard to the given illumination had been calculated, showed that the feeding response is distinctly intensity-dependent (Fig. 4). The animals are also capable of color discrimination independent of this intensity discrimination;P. brassicae prefers blue to other colors (e.g., orange, red and purple) with higher relative quantum numbers (Fig. 3) and distinguishes golden yellow and red from gray shades as well as from black and white (Fig. 5a, b).The results of subsequent spontaneous-choice experiments, using as stimuli monochromatic lights with known quantum flux, indicate that the various visually controlled functional categories of behavior can be assigned to the following spectral regions (Figs. 6, 8): 1. The open-space reaction corresponds to the UV and violet region, ca. 320–420 nm; 2. The feeding reaction corresponds to the blue region, ca. 420–500 nm, and the orange-red region, ca. 590–610 nm; 3. Egg-laying and drumming correspond to the green-yellow region, ca. 520–580 or 590 nm, respectively. The intensity dependence of the individual responses is again apparent in these experiments with monochromatic light stimuli (Figs. 7, 11, 12a).Even at very high intensities and when the content of the relevant wavelength is high, white light is practically ineffective for the feeding reaction (Fig. 9), drumming and egg-laying (cf. Results), regardless of its UV content. The open-space reaction, however, can be elicited by white light according to its UV content (Fig. 12 b).P. brassicae cannot be trained to give a feeding response to monochromatic light stimuli (Fig. 10).Experiments with mixtures of wavelengths have shown that the combination of the two maxima in the spectral sensitivity curve for the feeding reaction (=600 plus 447 nm) is just as effective as =447 nm alone (Fig. 13, left). Moreover, the mixture producing the hypothetical Pieris purple (=600 plus 370 nm) is no more or less effective in eliciting the feeding and open-space reactions than the more effective component for each of these reactions when presented alone (Fig. 13, right). With the mixture of =600 plus 558 nm, both the feeding reaction and drumming are distinctly reduced (Fig. 13, middle). This mixed color, unlike the other two mixtures tested, has a color quality different from that of the component colors.That the behavior ofP. brassicae is exclusively wavelength-specific can thus be ruled out. There are indications that wavelength-specific behavior and color vision are both present.Abbreviation RNQ relative number of quantaThis publication is dedicated to Professor Dr. Dr.h.c. H. Autrum on the occasion of his 80th birthday