Colour vision in nocturnal insects

Abstract

The ability to see colour at night is known only from a handful of animals. First discovered in the elephant hawk moth Deilephila elpenor , nocturnal colour vision is now known from two other species of hawk moths, a single species of carpenter bee, a nocturnal gecko and two species of anurans. The reason for this rarity—particularly in vertebrates—is the immense challenge of achieving a sufficient visual signal-to-noise ratio to support colour discrimination in dim light. Although no less challenging for nocturnal insects, unique optical and neural adaptations permit reliable colour vision and colour constancy even in starlight. Using the well-studied Deilephila elpenor , we describe the visual light environment at night, the visual challenges that this environment imposes and the adaptations that have evolved to overcome them. We also explain the advantages of colour vision for nocturnal insects and its usefulness in discriminating night-opening flowers. Colour vision is probably widespread in nocturnal insects, particularly pollinators, where it is likely crucial for nocturnal pollination. This relatively poorly understood but vital ecosystem service is threatened from increasingly abundant and spectrally abnormal sources of anthropogenic light pollution, which can disrupt colour vision and thus the discrimination and pollination of flowers. This article is part of the theme issue ‘Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods’.

High diversity of arthropod colour vision: from genes to ecology

“…Nocturnal or deep-sea species are often colour-blind but there are exceptions. For instance, large flower-visiting insects can discern colour even in starlight, as summarized by Warrant & Somanathan [95]. Specifically for nocturnal species, the increasing degree of artificial light pollution at night may pose challenges for their colour vision which may impair pollination (e.g.…”

Dim-light colour vision in the facultatively nocturnal Asian giant honeybee, Apis dorsata

“…That view changed with the discovery of colour vision in the nocturnal elephant hawkmoth Deilephila elpenor [7]. Subsequent confirmation from two other hawkmoths and a carpenter bee suggests that the ability to detect objects by the spectral component of light is an important aspect of dim-light vision in nocturnal flower-visiting insects as well as for nocturnal pollination [1,[7][8][9].…”

“…Seeing colour in the dark requires special visual adaptations-morphological, physiological and possibly neuronal [1,2]. In hawkmoths, this includes having superposition compound eyes whose low F-number optics produce a significantly brighter image [1], and neural summation strategies that increase the signal-to-noise ratio of vision [7,[10][11][12][13].…”

“…Seeing colour in the dark requires special visual adaptations-morphological, physiological and possibly neuronal [1,2]. In hawkmoths, this includes having superposition compound eyes whose low F-number optics produce a significantly brighter image [1], and neural summation strategies that increase the signal-to-noise ratio of vision [7,[10][11][12][13]. Interestingly, apart from hawkmoths, dimlight colour vision is also found in the nocturnal carpenter bee Xylocopa tranquebarica despite this bee-like all other bees-possessing apposition compound eyes better suited for vision in bright light [5,9,14].…”

OSpRad; an open-source, low-cost, high-sensitivity spectroradiometer

“…However, a growing number of species have been found to possess chromatic low-light vision, and sensitivity into the ultraviolet range (Kelber et al, 2017). This includes frogs and toads that have evolved cone-like-rods (Koskelainen et al, 1994; Yovanovich et al, 2017), geckos that possess three classes of rod-like-cones (Roth & Kelber, 2004), and nocturnal bees and hawkmoths that have the ability to discriminate colour down to star-light levels of illumination (Kelber et al, 2002; Warrant & Somanathan, 2022). Measuring the spectral composition of the night time light environment is therefore essential for understanding the potential effects on the vision of different species, and can be a useful tool for predicting the impact on various species’ visual ecology.…”