Abstract
The western flower thrips (Frankliniella occidentalis) is a serious pest in horticulture, feeding on leaf tissue and floral resources. Blue and yellow sticky traps are commonly used for monitoring and control in greenhouses. The mechanisms underlying the color preferences are largely unknown. The use of light-emitting diodes (LEDs) is a promising approach to increase the attractiveness of visual traps and to study the color choice behavior in insects. The color preferences of F. occidentalis were systematically investigated in a series of choice experiments with several LEDs from the ultraviolet (UV) and visible spectral range. Blue LEDs were most attractive, followed by green, while only a moderate attractiveness of UV was observed. Blue and green were identified as two separate attractive ranges. When light from blue and green LEDs was mixed, the attractiveness decreased compared to its single components. In conclusion, F. occidentalis exhibits two different wavelength specific behaviors towards blue and green. Compelling indications are provided that these behaviors are controlled by two photoreceptors maximally sensitive in the blue and green range with an inhibitory chromatic interaction between both. Since the known UV sensitive photoreceptor could be confirmed, a trichromatic photoreceptor setup is suggested for F. occidentalis. For advanced plant protection strategies, the results offer several opportunities to optimize monitoring or even develop mass trapping devices.
Highlights
Many insect species are adapted to unique plant resources while others forage on multiple resources, i.e., leaves, flowers, and fruits
All glass jars were kept in a climate cabinet (23 ◦ C, 63% RH, 16:8 h L:D photoperiod; Rubarth Apparate GmbH, Hannover, Germany). It was already noted in an earlier study that adult thrips from the glass jar rearing barely responded in light-emitting diodes (LEDs) choice experiments [10]
Our results show blue LED
Summary
Many insect species are adapted to unique plant resources while others forage on multiple resources, i.e., leaves, flowers, and fruits. Well-known examples are thrips species, e.g., western flower thrips (Frankliniella occidentalis), feeding on leaf tissue as well as on floral resources like pollen and nectar. Nutritional needs might change during the life cycle, color cues are, besides olfactory cues, important for detection of different plant characteristics. Visual-guided host plant detection is generally accepted as an indispensable binding link between potential olfactory orientation, which provides insufficient directional information, and selection upon host contact by herbivorous insects [1]. The importance of color cues for insect orientation has led to various applications in plant protection, since they allow the attraction without the involvement of any olfactory plant stimuli. Blue and yellow color traps are nowadays the most common method to detect a first infestation of thrips and whiteflies and to monitor the population development in vegetable and Insects 2020, 11, 423; doi:10.3390/insects11070423 www.mdpi.com/journal/insects
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