Visual orientation of the black fungus gnat, Bradysia difformis, explored using LEDs

Abstract

Fungus gnats occur worldwide with more than 1 700 described species. They can cause serious damages on ornamentals, crop plants, and edible mushrooms, and are considered to be a serious pest in the last years. Bradysia difformisFrey (Diptera: Sciaridae) represents a common species in Europe. Usually, yellow sticky traps are used for monitoring and control in greenhouses and fluorescent tube‐based light traps are additionally applied for control in mushroom cultivation. The importance of such visual trapping measures for efficient monitoring or alternative control increases in biological and integrated plant protection. However, detailed color preferences of fungus gnats are mostly unknown. We studied the visual orientation of B. difformis with light‐emitting diodes (LEDs) in a broad range of peak wavelengths from 371 nm (ultraviolet, UV) to 619 nm (amber). We determined attractive wavelengths in consecutive choice experiments in daylight and darkness. Highest numbers of adult B. difformis were attracted to UV radiation (382 nm) followed by green‐yellow light (532–592 nm). The responses to UV and the green‐yellow range were relatively unspecific and mostly independent from intensity. Combination of UV and yellow LEDs improved trapping efficacy compared to a single UV or yellow LED trap, as well as compared to a common yellow sticky trap. When both wavelengths were compared to a black surface to increase contrasts, the black surface was preferred over yellow, but was less attractive than UV. Thus, B. difformis displays two, probably wavelength‐specific, behaviors to UV radiation and green‐yellow light, with UV being the most attractive stimulus. These behaviors might be directly related to underlying photoreceptors, suggesting dichromatic vision in B. difformis.

Wavelength-Specific Behavior of the Western Flower Thrips (Frankliniella occidentalis): Evidence for a Blue-Green Chromatic Mechanism

“…The constructed light traps consist of housings (13 × 10 × 10 cm) made of polyvinylchloride plates (4 mm), as already used in previous studies [ 10 , 12 , 13 ]. Briefly, a colorless translucent acrylic glass plate with light scattering properties (Plexiglas ® , LED 0M200 SC, Evonik Industries AG, Essen, Germany) is located at the front.…”

“…Most LEDs were commercially available single-chip emitters but, as in a previous study, two specific multi-chip emitters were used which were equipped with additional cooling [ 13 ]. LEDs were operated as described in previous studies [ 10 , 12 ], allowing individual intensity adjustment. Using the same equipment and following the same protocols, all intensities were adjusted following Stukenberg and Poehing (2019).…”

“…Color choice studies using stimuli with different broadband reflection patterns commonly do not clearly separate intensity and wavelength-dependent responses. Therefore, the use of adjustable narrow-bandwidth LEDs has also turned out to be a suitable tool to study the color choice behavior of insects [ 10 , 11 , 12 , 13 ]. With one exception [ 10 ], the analyses carried out on the color preference of F. occidentalis are based exclusively on the use of reflective color traps.…”

High innate preference for black substrate in the chive gnat,Bradysia odoriphaga(Diptera: Sciaridae)

“…A strong brightness contrast may be found in nature between light plant stems, leaves and the dark substrate. The finding that adult fungus gnats, Bradysia difformis, significantly preferred black sticky traps over yellow ones, was interpreted that fungus gnat adults were searching for a convenient egg-laying substrate (Stukenberg et al, 2018). Based on this hypothesis, the spectral reflectance of the host plant ( Allium tuberosum ) and soil substrate close to root of the chive gnat was measured (Fig.…”

“…For example, the whitefly, Bemisia tabaci , some tephritid flies, and anthomyid flies, Strobilomyia spp. are particularly attracted by yellow sticky traps (Hill and Hooper, 2011; Jenkins and Roques 1993; Hou et al, 2006), whereas fungus gnat, Bradysia difformis , exhibit an innate colour preference for black (Stukenberg et al, 2018). Actually, in field experiments with coloured sticky traps chive gnat have already been successfully captured (Hong, 2016), but the quantitative analysis of the contribution of colour parameters such as hue and brightness to lure chive gnats has never been concerned so far.…”