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λ/4 Retarder Film Measurement from: Polarization of foliar reflectance – novel host plant cue for insect herbivores

Citation

Blake, Adam et al. (2019), λ/4 Retarder Film Measurement from: Polarization of foliar reflectance – novel host plant cue for insect herbivores, Dryad, Dataset, https://doi.org/10.5061/dryad.xgxd254bs

Abstract

Insect herbivores exploit plant cues to discern host and non-host plants. Studies of visual plant cues have focused on color despite the inherent polarization sensitivity of insect photoreceptors  and the information carried by polarization of foliar reflectance, most notably the degree of linear polarization (DoLP; 0-100%). The DoLP of foliar reflection was hypothesized to be a host plant cue for insects but was never experimentally tested. Here we show that cabbage white butterflies, Pieris rapae (Pieridae), exploit the DoLP of foliar reflection to discriminate among plants. In experiments with paired digital plant images, P. rapae females preferred images of the host plant cabbage with a low DoLP (31%) characteristic of cabbage foliage over images of a non-host potato plant with a higher DoLP (50%). By reversing the DoLP of these images, we were able to shift the butterflies’ preference for the cabbage host plant image to the potato non-host plant image, indicating that the DoLP had a greater effect on foraging decisions than the differential color, intensity or shape of the two plant images. Although previously not recognized, the DoLP of foliar reflection is an essential plant cue that may commonly be exploited by foraging insect herbivores.

Usage Notes

λ/4 retarder film measurements, description

Description of methods used to measure the wavelength-specific effects of the λ/4 retarder film (#88-253, Edmund Optics) on degree of linear polarization (DoLP) and axis of polarization (AoP). Includes figures, created with the R code in QWP_Retarder_Film_Measurement_R_code.R, showing the effect of rotation of λ/4 retarder film on the AoP and DoLP across different wavelengths of light.

QWP_Retarder_Film_Measurement_description.pdf

 

λ/4 retarder film measurements, raw data

136 transmission measurements taken through a λ/4 retarder film sandwiched between two polarizers. The measurements were taken at different rotations of the λ/4 retarder film (97°, 93°, 91°, 90°, 89°, 85°, 81°, 77°, 73°, 69°, 65°, 61°, 57°, 53°, 49°, 46°, 45°, 44°, 43°, 41°, 39°, 35°, 31°, 27°, 23°, 19°, 15°, 11°, 7°, 3°, 1°, 0°, -1°, -5°), and different angles between the axes of the two polarizers (0°, 45°, 90°, 135°).

QWP_Retarder_Film_Measurement_data.csv

 

λ/4 retarder film measurements, R code

The R code necessary to calculate the wavelength-specific effects of different rotations of the λ/4 retarder film on the AoP and DoLP, using the raw data contained in QWP_Retarder_Film_Measurement_data.csv. This code can also generate Figs. S5-7 in QWP_Retarder_Film_Measurement_description.pdf.

QWP_Retarder_Film_Measurement_R_code.R