Vision and visual navigation in nocturnal insects

Insects have extremely complex vision systems, despite their small size and relatively small number of neurons. Insects use their compound eyes to find food sources and catch prey, identify and avoid predators, move, swim, or fly in a complex three-dimensional environment, navigate to and from a nest using learnt visual land marks, and recognize and respond to conspecifics. These visual activities would be taxing enough, even in the bright, sunny world where many insects are active. However, such activities may initially appear difficult to the great majority of insects that are only active at night, when light levels might be up to 11 orders of magnitude lower. Nevertheless, despite the challenging lighting circumstances they encounter, we have started to recognize during the last 20 years that nocturnal insects carry out the same visual tasks as their diurnal relatives and with the same precision and accuracy. This remarkable discovery has sparked a renewed interest in the visual talents of nocturnal insects and a greater knowledge of how the neural system realizes these abilities. An eye must be able to capture enough light in order to see reliably. This essential criterion is easily met by a diurnal (day-active) animal that is suited for vision in bright sunshine. However, dependable eyesight cannot be ensured at night or at extreme water depths when light levels may be orders of magnitude lower (Warrant, 2008). This is by no means the norm, though, as many others have made significant investments in their eyesight and developed amazing adaptations to see well in low light (Laughlin, 1990). In order to demonstrate some of the fundamental concepts that insects utilize to process visual information in low light, this presentation features nocturnal insects. Insects that live in low light typically have extremely sensitive eyes. A dependable signal is only guaranteed if every photon that is captured is transduced effectively and consistently, even with extremely sensitive eyes capturing as many of the available photons as possible. The photoreceptors are responsible for this, and the degree of signal reliability at this level is determined by how well the receptors function as photodetectors. The efficiency of insect photoreceptors is remarkable, despite their imperfections. Optimal processing that minimizes the impacts of noise, such as summing visual signals in space and time, can further increase the trustworthiness of the signals they send to higher levels of the visual system. The insect’s behaviour is eventually guided by higher level processing of visual cues, such as the size and shape of learnt landmarks, the relative 1 movements of obstacles during flight, or the colour of nectar-bearing flowers. If higher-level processing is reliable in low light, nocturnal creatures may be able to see pretty well.