Blue–green opponency and trichromatic vision in the greenhouse whitefly (Trialeurodes vaporariorum) explored using light emitting diodes

Abstract

Visual orientation in the greenhouse whitefly (Trialeurodes vaporariorum Westwood, Hemiptera: Aleyrodidae) is the result of 'wavelength-specific behaviours'. Green-yellow elicits 'settling behaviour' while ultraviolet (UV) radiation initiates 'migratory behaviour'.Electroretinograms of the photoreceptors' spectral efficiency showed peaks in the green and the UV range and whitefly vision was said to be dichromatic.In order to study the visual behaviour of T. vaporariorum, nineteen narrow-bandwidth LEDs covering the UV-A and visible range were used in combination with light scattering acrylic glass screens in a small-scale choice arena under greenhouse conditions. Multiple-choice and dualchoice assays were performed, resulting in LED-based behavioural action spectra of settling (green) and migratory behaviour (UV). A potential inhibitory blue-green chromatic mechanism was studied by combining yellow with different blueish LEDs. Intensity dependencies were illustrated by changing LED intensities.Regarding the 'settling response', highest attraction was achieved by a green LED with a centroid wavelength of 550 nm, while a blue LED with 469 nm proved to be most inhibitory.Behaviour was distinctly intensity dependent. 'Migratory behaviour' was elicited the most by the UV LED with the shortest available wavelength of 373 nm. The results clearly prove the presence of a green and a yet undescribed blue sensitive photoreceptor and a blue-green opponent mechanism. Furthermore, empirical colour choice models were built and receptor peaks were estimated around 510 -520 nm (green), 480 -490 nm (blue) and 340 -370 nm (UV). Consequently, Trialeurodes vaporariorum possesses a trichromatic receptor setup.

A Greenhouse Test to Explore and Evaluate Light-Emitting Diode (LED) Insect Traps in the Monitoring and Control of Trialeurodes vaporariorum

“…Light is an important cue for insect orientation and host location [30,31]. The peak sensitivity of greenhouse whitefly optical receptors occurred at 525 nm around green light [14,[25][26][27]. The "opponent mechanism" of positive input from the green receptor coupled with negative input from the blue or UV receptor enables greenhouse whiteflies or aphids to differentiate various colors, and thus, respond differently [23,25].…”

“…Aphids possess two to three classes of photoreceptors that elicit either, a direct positive response or a negative response, and achieve color detection by comparing and integrating inputs from different spectra [23]. Recently, blue-green opponency and trichromatic vision were proven in the greenhouse whitefly [25]. The receptor peaks in the greenhouse whitefly were estimated to be approximately 510-530 nm (green), 480-490 nm (blue) and 340-370 nm (UV) [23,[25][26][27].…”

“…Recently, blue-green opponency and trichromatic vision were proven in the greenhouse whitefly [25]. The receptor peaks in the greenhouse whitefly were estimated to be approximately 510-530 nm (green), 480-490 nm (blue) and 340-370 nm (UV) [23,[25][26][27]. Regarding the "settling response", the greatest attraction was achieved by green LEDs and inhibited by blue LEDs [26].…”

“…The yellow target had a reflectance spectrum with little, or no, reflectance in the blue violet spectrum [22], and the highest green/blue ratio led to the most attraction to yellow. "Migratory behavior" was elicited the most by ultraviolet (UV) light [25,[27][28][29]. UV light was attractive to the greenhouse whitefly, especially in the dark, but it was less attractive than the green-yellow spectrum [8,13,16].…”

“…Most previous cage studies of LED traps used green and UV LEDs in their tests [13,14,16,17,19]. The most sensitive behavioral spectrum is not always the most sensitive light receptor spectrum [25]; it is the integration of visual stimuli inputs in the central nervous system that results in the peculiar phototactic response exhibited by the species [8]. The landing response is substantially influenced by a variety of factors, in addition to light wavelengths, including light intensity, the contrast between light source intensity and color to that of ambient light, and the state or physiology of the insects [5,7].…”