Supple et al. investigate the spectral sensitivity of motion-sensitive descending neurons (DNs) connecting the brain to thoracic motor centers in butterflies. Optic flow-sensitive DNs are spectrally b...

Supple et al. investigate the spectral sensitivity of motion-sensitive descending neurons (DNs) connecting the brain to thoracic motor centers in butterflies. Optic flow-sensitive DNs are spectrally b...

Ecological interactions exert contrasting evolutionary pressures on sympatric Morpho butterflies, promoting convergence in iridescence but divergence in chemical cues, illustrating how ecological inte...

We investigated the role of vision in host-seeking behaviour by Philaenus spumarius, the main European vector of Xylella fastidiosa, through an integrated anatomical, optical, physiological, and beha...

Insect compound eyes adapt in response to average stimulus intensity, but the adaptation is mediated also by intrinsic circadian rhythms and abiotic factors like temperature, which are indirectly related to the stimulus. We studied the effect of light, circadian rhythm, temperature and body size on light adaptation in Grapholita molesta (GM), Lobesia botrana (LB) and Cydia pomonella (CP) (Lepidoptera: Tortricidae). These moths have superposition compound eyes with identical trichromatic photoreceptor sets and temporal resolution; however, the adults are sexually active before (GM), during (LB) or after (CP) sunset, and experience very different light intensity and temperature variations during their activity period. Their eyes were examined with infrared pupillometry, light microscopy and micro-CT. The compound eyes are very small to medium-sized, with a clearly visible superposition pupil. The pupil reflectance of adults entrained to a 12/12 h light/dark cycle for 2 days maintained the entrained rhythm for days, closing and opening during the subjective day and night, respectively. Circadian rhythm was the most robust in CP. A fully open pupil was forced to close with a light pulse, and pupil brightness changes were monitored at 15 and 22 °C. The experiment revealed complex and different pupil dynamics among species at both temperatures. GM, the smallest species, was most affected by the lower temperature. The experimental paradigm can be used for high-throughput, non-invasive monitoring of multiple species’ response to climate change, and to chemical and light pollution.

Compound eyes deliver a vast stream of information to the tiny insect brains. To maximize the information content and minimize the redundancy of neural signals, insect eyes are built so to encode the relevant and filter out the unimportant elements of the visual environment. Terrestrial habitats have a predictable spatio-spectral structure, which can be matched by the distribution of photoreceptors with different spectral sensitivities across the retina. Here, we investigate the retinal organization of the nymphalid butterfly Heliconius melpomene using single-cell recordings, immunohistochemistry and eye shine imaging. The ventral retina is enriched with ommatidia, which contain red screening pigments that shape the spectral sensitivity of basal red receptors R9, while their long visual fibre photoreceptors R1&2, expressing a long-wavelength (L) opsin, are synaptically inhibited by R9 and directly participate in colour vision. These G + R– receptors frequently co-express the L opsin with the blue (B) or ultraviolet (U) opsin. U&L opsin-co-expressing R1&2 are scarce, while B&L co-expression is frequent in the ventral ommatidia and gradually diminishes towards the eye equator, where G + R– receptors express the L opsin only. In this region, G + R– receptors are further inhibited by blue-sensitive receptors. With electrophysiology matching immunohistochemistry, we reveal the fine tuning of spectral sensitivity of a single photoreceptor class across the dorso-ventral axis of the butterfly compound eye. Similar tuning is found in other nymphalid butterflies across the phylogeny, suggesting that this adaptation is ancestral and confers an advantage to those diurnal nymphalids, equipped with the cellular toolkit for colour vision in the red.