Insect visual sensitivity to long wavelengths enhances colour contrast of insects against vegetation

Abstract

The sensitivity of animal photoreceptors to different wavelengths of light strongly influence the perceived visual contrast of objects in the environment. Outside of the human visual wavelength range, ultraviolet sensitivity in many species provides important and behaviourally relevant visual contrast between objects. However, at the opposite end of the spectrum, the potential advantage of red sensitivity remains unclear. We investigated the potential benefit of long wavelength sensitivity by modelling the visual contrast of a wide range of jewel beetle colours against flowers and leaves of their host plants to hypothetical insect visual systems. We find that the presence of a long wavelength sensitive photoreceptor increases estimated colour contrast, particularly of beetles against leaves. Moreover, under our model parameters, a trichromatic visual system with ultraviolet (λmax = 355 nm), short (λmax = 445 nm) and long (λmax = 600 nm) wavelength photoreceptors performed as well as a tetrachromatic visual system, which had an additional medium wavelength photoreceptor (λmax = 530 nm). When we varied λmax for the long wavelength sensitive receptor in a tetrachromatic system, contrast values between beetles, flowers and leaves were all enhanced with increasing λmax from 580 nm to at least 640 nm. These results suggest a potential advantage of red sensitivity in visual discrimination of insect colours against vegetation and highlight the potential adaptive value of long wavelength sensitivity in insects.

Unravelling the mystery of red flowers in the Mediterranean Basin: How to be conspicuous in a place dominated by hymenopteran pollinators

“…UV‐red floral colour increased the chromatic contrast by the excitation of short‐wavelength photoreceptors of these pollinators without affecting their conspicuousness to red‐sensitive pollinators, as glaphyrid beetles. This is consistent with its well‐known preference for red colours (Wang et al, 2022). Therefore, the additional reflectance in the UV might represent a signalling strategy to also target hymenopterans.…”

“…To the best of our knowledge, there are no visual sensitivity functions available based on behavioural data for coleopterans. However, the fact that our model species of beetle, Pygopleurus israelitus , showed a long wavelength photoreceptor with a longer peak sensitivity than those of lepidopterans (580 nm and 560 nm, respectively; Koshitaka et al, 2008; Martínez‐Harms et al, 2012), suggests that coleopterans would be even better adapted to red flowers, as suggested by several authors (Streinzer et al, 2019; Wang et al, 2022). Moreover, the reflectance spectra of UV‐red flowers and the floral guide of pure red patterned flowers possess marker points nearer to the short wavelength maximum colour discrimination of hymenopterans, allowing for better discrimination (Chittka & Menzel, 1992; Dyer et al, 2012).…”

“…Although rare, hymenopterans, including a species of Andrenidae, are known to display an additional long‐wavelength photoreceptor (Peitsch et al, 1992). Thus, this would not rule out that other species of pollinating hymenopterans of the Mediterranean Basin may possess this fourth photoreceptor, which would help to perceive red‐flowered species irrespective of the UV reflectance (Wang et al, 2022). Furthermore, it is found that Sardinian populations of Bombus terrestris showed strong preference for red flower colour but they did not possess an additional long‐wavelength photoreceptor (Skorupski et al, 2007).…”

“…Lastly, a generalization of the ‘bee avoidance’ hypothesis could be applied to Mediterranean species with red flowers (Coimbra et al, 2020). Based on the spectral sensibility of the Mediterranean Basin pollinators, certain insect groups of coleopterans and lepidopterans can be considered as ‘red sensitive’, while hymenopterans and dipterans have a low sensibility in the red region and can be considered as ‘red insensitive’ pollinators (Martínez‐Harms et al, 2012; van der Kooi et al, 2021; Wang et al, 2022). Thus, we predict that species pollinated by red‐sensitive insects would show red flowers poorly perceived by red‐insensitive pollinators (Camargo et al, 2019; Lunau et al, 2011).…”

The Effect of Trap Color on Catches of Monochamus galloprovincialis and Three Most Numerous Non-Target Insect Species

“…Although beetles lost their sensitivity to blue wavelengths millions of years ago, some of them were able to overcome this loss through opsin duplications, particularly UV opsins [ 32 , 33 ]. Furthermore, some insects were also found to be sensitive to the violet (~420 nm) and red (>600 nm) regions of the light spectrum [ 33 , 34 , 35 ]. However, insect response/sensitivity to different wavelengths and reflectance intensity seems to be species- and sex-specific [ 30 , 34 , 36 , 37 , 38 ].…”