Flying Drosophila suzukii navigate using celestial visual cues

Spotted-wing drosophila (SWD; D. suzukii) is a tiny yet potent insect pest that causes enormous damage to berries and stone fruit worldwide. The species has rapidly expanded its range in recent decades, motivating efforts to understand how it moves at a landscape scale. Flies have the energy to fly for multiple hours, yet can only detect a fruit target from a few meters away, raising the question of how they direct their movement in the absence of local attractive cues. We investigated the possibility that SWD uses stable visual cues from the sky to maintain an extended straight flight heading – a navigational capacity known to enable long-distance dispersal in other insects. Using custom-built lab arenas, we tracked extended flight trajectories of individual tethered D. suzukii steering relative to a visual cue mimicking the sun. We found that flies maintained stable, straight-line flight paths at arbitrary headings relative to the sun stimulus. In complementary field experiments, we released thousands of flies from a central point and tracked their arrival across a grid of computerized camera traps. We found that flies disperse radially, covering 20m in a minute. Taken together, these data demonstrate that D. suzukii has a capacity for extended straight-line navigation at arbitrary headings relative to a visual stimulus. Our findings suggest that SWD can disperse a kilometer in an hour, significantly farther than prior estimates.