Multimodal Stimulation of Colorado Potato Beetle Reveals Modulation of Pheromone Response by Yellow Light

Abstract

Orientation of insects to host plants and conspecifics is the result of detection and integration of chemical and physical cues present in the environment. Sensory organs have evolved to be sensitive to important signals, providing neural input for higher order multimodal processing and behavioral output. Here we report experiments to determine decisions made by Colorado potato beetle (CPB), Leptinotarsa decemlineata, in response to isolated stimuli and multimodal combinations of signals on a locomotion compensator. Our results show that in complete darkness and in the absence of other stimuli, pheromonal stimulation increases attraction behavior of CPB as measured in oriented displacement and walking speed. However, orientation to the pheromone is abolished when presented with the alternative stimulation of a low intensity yellow light in a dark environment. The ability of the pheromone to stimulate these diurnal beetles in the dark in the absence of other stimuli is an unexpected but interesting observation. The predominance of the phototactic response over that to pheromone when low intensity lights were offered as choices seems to confirm the diurnal nature of the insect. The biological significance of the response to pheromone in the dark is unclear. The phototactic response will play a key role in elucidating multimodal stimulation in the host-finding process of CPB, and perhaps other insects. Such information might be exploited in the design of applications to attract and trap CPB for survey or control purposes and other insect pests using similar orientation mechanisms.

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

“…Green and yellow were the most attractive lights for L. decemlineata and darkness was unattractive. L. decemlineata was positively phototactic when offered dark and light cues [24]. In contrast, D. abbreviatus did not show a strong phototactic response.…”

“…The multimodal stimulation study performed with Colorado potato beetle, Leptinotarsa decemlineata, in a similar dual-choice arena revealed subordination of chemotaxis to phototaxis [24]. Green and yellow were the most attractive lights for L. decemlineata and darkness was unattractive.…”

“…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.…”

“…In all experiments, LEDs were the only source of illumination in the room. Responses were recorded for three consecutive 2-min periods [24]: in the air stream alone (control), in the air stream plus other experimental stimuli (test), and in the air stream after removal of the experimental stimuli (end-control). The eolic stimulation (air stream) was supplied during control, test, and end-control periods, but chemical and photic stimuli were only supplied during the test period.…”

“…Although the interaction of vision and olfaction in D. abbreviatus orientation has not been studied, several authors have investigated multimodal stimulation in other insects [17], [18], [19], [20], [21], [22], [23], [24]. Here we investigated the response of male and female D. abbreviatus to narrow bandwidths of visible light emitted by LEDs offered alone and in combination with olfactory stimuli.…”