Giant water bugs (Hemiptera: Belostomatidae) have highly sensitive eyes for amphibious vision

The visual systems of amphibious insects function in two distinct environments: air and water. Although we understand how the optics of visual systems change to meet amphibious demands, it is unknown how the physiological properties of visual systems adapt to support amphibious vision. Giant water bugs (Hemiptera: Belostomatidae) start as obligately aquatic nymphs and then transition to amphibious adults that carry out visually-guided behaviors in air and water, making them an ideal system in which to ask this question. To address how the visual physiology of amphibious insects supports behaviors in air and water, we used electroretinography (ERG) to characterize the irradiance sensitivity (VlogI) and temporal sampling rates (flicker fusion frequency) of eyes from three species of giant water bug: Belostoma flumineum, Lethocerus medius, and Abedus herberti. We found that all three species have similar irradiance sensitivities that span over 5 orders of magnitude. Our results also indicate that all three species have similar temporal sampling rates when dark-adapted (50-60 Hz), but different rates when light-adapted (60-90 Hz). In a focused study on the spectral sensitivity of B. flumineum, we inferred the presence of one spectral class of photoreceptor. We also investigated the neuroanatomy B. flumineum and found the optic neuropils are organized similarly to those of other flying insects. Here, we show that the visual systems of amphibious insects support their ecology with broad irradiance sensitivity, which may allow these insects to efficiently transition between water and air, and temporal sampling rates high enough to resolve fast-moving prey.