Spectral preference and temporal modulation of photic orientation by Colorado potato beetle on a servosphere

Abstract

The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), is a diurnal insect that strongly relies on visual cues to guide its walk. In the present study, we investigated the orientation behavior of non-diapausing walking CPB in response to emissive colors produced by light emitting diodes (LEDs) in a dual choice arena adapted to a servosphere, where the only illumination available came from the photo-stimuli. Our results demonstrate that CPB show positive phototactic behavior when stimulated with different wavelengths of light; they preferred to orient towards white (420-775 nm), ultraviolet (UV) (351 nm), blue (472 nm), green (570 nm), yellow (585 nm), orange (590 nm), and red (660 nm) over darkness when both alternatives were offered, but no orientation responses were elicited by infrared (940 nm). Both males and females preferred yellow and green over other colors, but did not show any particular preference between them, thus correlating with their preference for wavelengths reflected by vegetation. Sexual differences were noted in that male CPB preferred white over either red or UV, whereas female CPB did not show any preferences when offered these colors. Female CPB preferred UV and blue over red, whereas males showed no preferences when these colors were offered. Colorado potato beetles turned at higher angles and performed more tortuous walks in complete darkness and when infrared vs. darkness were offered compared with the rest of the colored lights. Both sexes preferred continuous over pulsed yellow light. Colorado potato beetles subjected to pulsed yellow light showed a temporal alteration of their walking performance by walking less, slower, and turning at a higher rate. The results are discussed with regard to the role of color in the CPB attraction to host plants and conspecifics as well as the role of intermittent photic stimuli in their orientation behavior. The information provided here provides a basis for the improvement of trapping devices for detection and survey of incipient or invasive CPB, and development of alternate control strategies for this important pest of potatoes and other solanaceous crops.

Olfactory Cues Are Subordinate to Visual Stimuli in a Neotropical Generalist Weevil

“…As the walls of the corridors were made of reflective material, it is possible that the LED lights could have been taken as background illumination by the insects. The adaptive value of phytophagous insects' preference for green and yellow wavelengths reflected by most plant foliage including citrus leaves [38] has been discussed in previous works [39], [16]. It is believed that attraction of herbivorous insects to green and yellow wavelengths allows them to discriminate foliage (reflectance range of 500 to 580 nm) from non-foliage hues (peaking at <500 nm or >580 nm) [39].…”

“…The observation system used in this study was tested previously with L. decemlineata [16], [24] and consisted of a modified version of a crossroad arena [28]. It comprised two perpendicular corridors (length 36 cm, wide 7 cm, height 14 cm) made of acrylic plastic (polymethyl methacrylate) walls (thick 5 mm) (Precision Plastics Inc, Beltsville, MD, USA) fitted over a servosphere but allowing the sphere to rotate freely underneath the corridors (Fig.…”

“…Maximum peaks and centroid wavelengths did not differ by more than 5 nm, i.e., wavelength shapes were highly symmetric. Peak wavelengths tested occurred at 351 (ultraviolet), 472 (blue), 570 (green), 585 (yellow) and 660 nm (red) [16]. Color names correspond to the subjective visual sensation produced on the human eye by these wavelengths.…”

“…One set consisted of experiments in which each insect was given a choice between two monochromatic LED pairs in still air (group 1). Responses of weevils to colored lights were recorded for 3 min [16]. The other set of experiments comprised 4 series of bioassays (group 2).…”

“…Colors emitted by light emitting diodes (LEDs) do not depend on the illuminating conditions and allow for selection and comparison of spectra of experimental light sources. Recently, a multiple choice arena adapted to a servosphere was developed to observe walking of Colorado potato beetle [ Leptinotarsa decemlineata (Say)] responding to colored LEDs [16].…”