Visual control of wing beat frequency in Drosophila.

The present study shows that the wing beat frequency of Drosophila is visually controlled and modulated in response to different optomotor stimuli. Whereas rotational large field stimuli do not appear to modulate wing beat frequency, single rotating vertical stripes increase or decrease wing beat frequency when moving back-to-front or front-to-back, respectively. Maximal modulations occur at lateral stripe positions. Expansion stimuli eliciting the landing response cause a marked increase in wing beat frequency. Parameters of this frequency response depend in a graded fashion on certain stimulus properties, and the frequency response co-habituates with the landing response. Several results indicate that the frequency response is an integral component of the landing response, although it can also occur when the characteristic front leg extension is not observed. The complex spatial input integration underlying the frequency response and other motor components of the landing response cannot easily be explained by a system of large field integration units, but might indicate the existence of local expansion detectors.