Colour Response in Western Flower Thrips Varies Intraspecifically

Abstract

Discrepancies in the published research as to the attraction of the economically important pest western flower thrips (WFT) to different colours confounds the optimisation of field traps for pest management purposes. We considered whether the different experimental conditions of independent studies could have contributed to this. Therefore, the behavioural response (i.e., landings) to different colour cues of two WFT laboratory populations from Germany (DE) and The Netherlands (NL), which had previously been independently shown to have different colour preferences, were tested in the same place, and under the same experimental conditions. Single-choice wind tunnel bioassays supported previous independent findings, with more of a NL population landing on the yellow LED lamp (588 nm) than the blue (470 nm) (p = 0.022), and a not-statistically significant trend observed in a DE population landing more on blue compared to yellow (p = 0.104). To account for potential original host rearing influences, both populations were subsequently established on bean for ~20 weeks, then yellow chrysanthemum for 4–8 and 12–14 weeks and tested in wind tunnel choice bioassays. Laboratory of origin, irrespective of the host plant rearing regime, remained a significant effect (p < 0.001), with 65% of the NL WFT landing on yellow compared to blue (35%), while 66% of the DE WFT landed on blue compared to yellow (34%). There was also a significant host plant effect (p < 0.001), with increased response to yellow independent of laboratory of origin after rearing on chrysanthemum for 12–14 weeks. Results suggest that differing responses of WFT populations to colour is, in this case, independent of the experimental situation. Long-term separate isolation from the wild cannot be excluded as a cause, and the implications of this for optimising the trap colour is discussed.

Colour vision in thrips (Thysanoptera)

“…A more systematic approach is needed to understand the fundamentals of thrips colour vision so that we can identify the optimal stimuli for attracting pest species for monitoring and mass trapping [97,109]. This has improved in recent years, but standardization of methods is still needed to resolve ambiguities.…”

“…What remains to be determined is how good thrips colour discrimination is and whether they indeed possess true colour vision. The degree of attraction to a colour varies among different thrips species, although intra-specific variation of colour attraction is also found in widely studied species like F. occidentalis [109]. Unfortunately, many of the behavioural studies evaluating thrips colour attraction are based on spontaneous behaviours including orientation and landing on different coloured stimuli, which limits interpretation of results in a broader context.…”

Tracking the flight and landing behaviour of western flower thrips in response to single and two-colour cues

“…However, there is ongoing debate regarding the most attractive colour to optimize WFT catches, especially between blue and yellow 2 , 6 . To date, much of the research on WFT trapping is based on measuring the number of landings on a target 2 , 7 . This end-point data quantifies the overall efficacy of colour cues but provides no information about how their behaviour is influenced when approaching visual cues.…”

“…For this, a dedicated system was developed to meet the challenges of tracking and quantifying free-flying WFT, including optimizing the detection sensitivity for tiny targets, fast video processing to enable real-time performance at high frame rates, and reliable detection against both a back-illuminated LED lamp surface (the target) and a dark background (surroundings). The tracking system was used in a wind tunnel similar to end-point studies performed previously to study the efficacy of different colours to attract thrips 7 , 23 . As a result of those studies, the emphasis here was on behaviour towards the highly attractive yellow and UV.…”

“…In a first experiment, the response of WFT to yellow (587 nm peak wavelength), blue (470 nm) and green (533 nm) was evaluated either as single-colour or colour combinations with the respective LEDs side-by-side in two halves of a LED lamp. In a second experiment, a UV-A light (369 nm) was included with yellow and green to test the hypothesis, based on earlier observations 7 , that UV-light has a role in the landing of WFT on visual cues.…”