The visual system of a nocturnal long-distance migrant, the Australian Bogong moth.

Abstract

The Australian Bogong moth (Agrotis infusa) is a small noctuid moth that undertakes annual, nocturnal migrations of up to 1000 km to escape the summer heat of its breeding grounds. The moths travel to cool alpine caves, where they enter a dormant state (aestivation) before returning to reproduce and die. During migration, their brains integrate magnetic and visual cues to guide their flight direction. While the Bogong moth's neurobiology is increasingly understood, its visual system has remained unexplored. Here, we describe the morphology, ultrastructure, optics, and visual opsins of the Bogong moth's compound eyes and ocelli. Using light and electron microscopy, micro-computed tomography, in situ hybridization, and spectral absorbance measurements, we show that the compound eyes are typical superposition eyes with a tiered rhabdom, similar to other noctuid moths. The ocelli are small but structurally complex, featuring a two-tiered retina with spectrally distinct receptor cells and a lens forming a focused image on the ocellar retina. At the molecular level, the Bogong moth expresses three canonical opsins (UV, blue, and long-wavelength) and an additional red-shifted long-wavelength opsin, suggesting enhanced sensitivity to long-wavelength light. These opsins exhibit distinct expression patterns across the compound eyes, indicating functionally distinct dorsal and ventral eye hemispheres. Overall, the Bogong moth's visual system displays multiple adaptations to nocturnal vision. These features, likely shared across noctuid moths, may have contributed to the evolution of the exceptional navigational abilities during long-distance migrations in dim light that define the Bogong moth, but which are also widespread across noctuid moths.