Colour Response in Western Flower Thrips Varies Intraspecifically

SIMPLE SUMMARY: The western flower thrips (WFT) is a major glasshouse pest worldwide. Colour and odour are used to attract WFT to traps for monitoring in pest management. However, the use of colour attraction for surveillance, or its potential as a control tool for mass trapping, has not progressed due to ongoing debate about the optimal colour. Blue is commonly used for monitoring, but yellow can also be preferred over blue, confounding the implications for field application. As methodological differences amongst studies could cause this discrepancy, in the present study we evaluated populations from Germany (DE) and the Netherlands (NL) that had previously expressed different preferences for blue and yellow. Examining the behavioural response of WFT to blue or yellow LEDs in a wind tunnel by using the same methodology and facilities, the two populations maintained their original differential preferences. This remained after several generations under common conditions, although a significant increase in attraction to yellow was observed for both populations when reared on yellow-flowered chrysanthemum plants. This is the first report demonstrating that WFT populations can differ in their colour preferences even under the same experimental circumstances. Given that research is typically achieved with populations isolated from the wild for many generations, caution is still needed when extrapolating this to field situations. 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.