LED based trapping of whiteflies and fungus gnats : from visual ecology to application

Abstract

Yellow sticky card traps are used for monitoring and control of the greenhouse whitefly (Trialeurodes vaporariorum) and the black fungus gnat (Bradysia difformis) in greenhouses. The use of light emitting diodes (LEDs) has turned out as a promising approach to increase the efficiency and reliability of visual traps. Moreover, LEDs provide the possibility to study the visual behaviour and colour processing of insects. On the background of improving visual traps, the aim of this thesis was to investigate the colour choice behaviour of T. vaporariorum and B. difformis, thereby connecting basic experimental research with applicable aspects. Finally, an LED enhanced yellow sticky trap should be developed and evaluated. In chapter 1 and 2, the visual behaviour of T. vaporariorum and B. difformis was studied with a number of LEDs from the ultraviolet (UV) and visible light range of the spectrum in combination with light scattering acrylic glass screens. Several choice assays with different LED colours and combinations were performed in a small-scale choice arena under greenhouse conditions. It was revealed, that T. vaporariorum possesses a yet undescribed photoreceptor sensitive for blue light and an inhibitory blue-green chromatic mechanism. This mechanism controls a ‘wavelength-specific behaviour’ used for host plant detection. Besides this chromatic processing, the behavioural response is distinctly intensity dependent. Based on subsequent modelling, photoreceptor peaks were estimated around 510 - 520 nm (green), 480 - 490 nm (blue) and 340 - 370 nm (UV). Consequently, T. vaporariorum possesses a trichromatic receptor setup. B. difformis shows two different, probably ‘wavelength-specific’, behaviours to UV radiation and green-yellow light, with UV being the most attractive stimulus. The two behaviours might be directly related to underlying photoreceptors, suggesting dichromatic vision in B. difformis. Moreover, the results show the superior attractiveness of especially UV LEDs compared to conventional yellow traps. In chapter 3, LED enhanced yellow traps were constructed which combine yellow cards with specific edge lighting acrylic glass equipped with green high-power LEDs in a frame. Traps were equipped with cameras and an LED illumination system to generate transmitted and incident light images at dark night-time conditions which enabled the subsequent identification and counting of whiteflies and fungus gnats. The efficiency of these traps was compared with conventional yellow traps in small-scale tomato crop stands. The results show a significantly increased efficiency of the developed LED enhanced traps for whiteflies compared to yellow traps in experiments with high population densities and in choice situations with both trap types. A higher efficiency for fungus gnats was observed throughout. The obtained images allowed reliable counting of both pests, comparable with manual counting on traps.