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.

Keywords: Frankliniella occidentalis; behaviour; colour choice-test; thrips; trapping; wind tunnel.

Figure 1

Diagram showing the derivations of WFT colonies from Wageningen, The Netherlands (NL) and Hannover, Germany (DE) from the original base colonies and used in Experiments i–iii.

Figure 2

The wind tunnel setup used for the WFT behavioural experiments viewed from different perspectives illustrating: (A) The complete equipment arrangement; (B) the yellow stimulus, release container and wind direction; (C) the release container in relation to the LED stimulus (blue). Red arrow, LED lamp (dome); green arrow, insect release platform; yellow arrow, insect release container; blue arrows, wind direction inside the wind tunnel; black arrow, general ceiling illumination provided for the wind tunnel (includes wavelengths in the visible light spectrum and UV-A light).

Figure 3

Aspects of the 3D printed dome housing the LEDs. (A) Frontal view showing the interior covered with aluminium foil, red arrow shows the division inside the dome. (B) Frontal view with the frame attached. (C) LED lamp with the diffusing glass plate and transparent propylene sheet with sticky glue. (D) Removable frame where the transparent sticky plastic was placed for catching the WFT. (E) Back side of the dome showing the four visible orifices where LEDs were placed. (F) LED lamp inside the wind tunnel shining a yellow and blue LED from inside the dome.

Figure 4

Experiment i: Mean percentage of Dutch WFT (NLc) caught on the sticky glass plate of the LED lamp with different colours six hours after release. N = 4 replicates. Error bars are 95% confidence intervals. Peak wavelength of LEDs used: Pink (UV-A 369 nm), Violet (422 nm), Blue (477 nm), Cyan (502 nm), Green (529 nm), Yellow (588 nm), Red (651 nm). Each LED was presented as a single choice. All information from this figure is provided in Supplementary Table S6.

Figure 5

Experiment ii: Mean percentage of German WFT (DEc) caught on the sticky glass plate of the LED lamp with blue or yellow light six hours after the release of the insects. Error bars are 95% confidence intervals. Peak wavelength of LEDs: Blue (477 nm), Yellow (588 nm). Each LED was presented as a single choice. All information from this figure is provided in Supplementary Table S7.

Figure 6

Experiment iii, analysis a: Stacked bar chart showing the percentages of WFT found on the yellow or blue light per laboratory of origin and rearing regime out of the total number of thrips that landed on the sticky glass plate of the LED lamp. Peak wavelength of LEDs: Blue (477 nm), Yellow (588 nm). DEb: colony of German WFT reared on bean pods for ~20 weeks; DEbc 4-8: DEb colony transferred and reared on yellow-flowered chrysanthemum plants for 4 to 8 weeks; DEbc 12-14: continuation of colony DEbc 4-8 until reaching 12 to 14 weeks reared on yellow-flowered chrysanthemum plants. NLb: colony of Dutch WFT reared on bean pods for ~20 weeks; NLbc 4-8: NLb colony transferred and reared on yellow-flowered chrysanthemum plants for 4 to 8 weeks; NLbc 12-14: continuation of colony NLbc4-8 until reaching 12 to 14 weeks reared on yellow-flowered chrysanthemum plants. All information from this figure including mean percentages and 95% confidence intervals is provided in Supplementary Table S8.

Figure 7

Experiment iii, analysis b: Stacked bar chart showing the percentages of WFT that left the release container as per the laboratory of origin and rearing regime for each of the four categories in which the WFT was grouped inside the wind tunnel. Peak wavelength of LEDs: Blue (477 nm), Yellow (588 nm). DEb: colony of German WFT reared on bean pods for ~20 weeks; DEbc 4-8: DEb colony transferred and reared on yellow-flowered chrysanthemum plants for 4 to 8 weeks; DEbc 12-14: continuation of colony DEbc 4-8 until reaching 12 to 14 weeks reared on yellow-flowered chrysanthemum plants. NLb: colony of Dutch WFT reared on bean pods for ~20 weeks; NLbc 4-8: NLb colony transferred and reared on yellow-flowered chrysanthemum plants for 4 to 8 weeks; NLbc 12-14: continuation of colony NLbc4-8 until reaching 12 to 14 weeks reared on yellow-flowered chrysanthemum plants. All information from this figure including mean percentages and 95% confidence intervals is provided in Supplementary Table S9.