This news release is available in Japanese.
How do nocturnal insects forage so successfully in the twilight and darkness? A new study by Simon Sponberg and colleagues suggests that the vision of the hawkmoth, Manduca sexta, which hovers in place while it feeds on nectar at dawn and dusk, is finely attuned to the swaying of flowers in the breeze. These findings imply that both the sight and flight of the hawkmoth likely evolved to match the movements of flowers -- their only source of food -- perfectly, helping to explain how the nimble insects are able to track wind-tossed flowers under low-light conditions. The researchers hypothesized that the insects, which have tiny brains, may compensate for dim conditions by slowing their visual processes. But Sponberg et al. also knew that such trade-offs reduce individuals' response times. So they tested hovering hawkmoths with an artificial flower on a robotic arm, which was programmed to move side-to-side at various frequencies. The researchers found that the moth's tracking responses were about 17% slower in dark, moonlit conditions compared to brighter, early-dusk light. However, the researchers also discovered that the movement of the artificial flower was a significant factor: When it moved at a frequency higher than 1.7 Hertz, the hawkmoths had trouble tracking it. When it moved at frequencies less than 1.7 Hertz, on the other hand, the moths had very little trouble. Sponberg and his team then analyzed the movements of some of the hawkmoths' favorite flowers as they blew in the wind, finding that 94% of the flowers' motion remained below 1.7 Hertz. Taken together, the findings suggest that hawkmoths are able to avoid the pitfalls of slower visual processing because their sight is precisely adapted to the light and movement conditions of their natural environment. A Perspective article by Eric Warrant explains the study in greater detail.
Article #22: "Luminance-dependent visual processing enables moth flight in low light," by S. Sponberg; J.P. Dyhr; R.W. Hall; T.L. Daniel at University of Washington in Seattle, WA; S. Sponberg at Georgia Institute of Technology in Atlanta, GA; J.P. Dyhr at Northwest University in Kirkland, WA.