2.2.2. LED wavelength sources

An LED lamp was developed to provide a visual cue for L. rugulipennis in the wind tunnel. The lamp consisted of a 3D‐printed black cone (18.5 cm diameter with a diffusing glass plate in the front (11.5 cm diameter) and the inside was covered with aluminum foil (Fig. S1). For each trial, a layer of sticky glue P300I35 (Intercol, Industrial adhesives, NL) was applied on a 100 μm transparent polypropylene sheet (Staples Solutions, NL) and placed on the exterior of the glass plate (Edmund Optics Ltd., York, UK) (Fig. S1). The LED source was placed on the back of the cone, shining through the glass plate, and sticky sheet. The lamp was connected to a holder shining downward at an angle of 45° to the floor of the wind tunnel. The center of the lamp was fixed at 60 cm from the floor, and the insect release platform was placed 70 cm from the base of the lamp and at a height of 8 cm. The selected wavelengths were 365, 385, 405, 420, 470, 490, 530, 590, 650, and 720 nm. Although there are several definitions of the wavelength ranges of colors, the color categories as defined by CIE (https://cie.co.at/publications/cie-collection-photobiology-photochemistry-1999) was adopted for this study. For example, the definition of insect visible UV‐A range is between 315 and 400 nm, and different insects have different optimal UV‐A visibility and response. Therefore, 365 nm was selected as the lowest UV‐A visible wavelength in this study because of safety reasons, particularly, where human exposure is involved. Generally, the wavelengths were selected based on LED color availability and insect visibility as determined by Briscoe and Chittka. ²⁴ The brightness levels tested were 4.48 and 5.86 μmol photons per steradian m⁻² s⁻¹. The emission spectra of the LEDs and the brightness of the light sources were measured inside the wind tunnel using a broadband spectroradiometer Specbos 1211UV (JETI Technische Instrumente GmbH, Germany).