Visuomotor Response to Object Expansion in Free-Flying Bumble Bees

Abstract

The flight control systems of flying insects enable many kinds of sophisticated maneuvers, including avoidance of midair collisions. Visuomotor response to an approaching object, received as image expansion on insects’ retina, is a complex event in a dynamic environment where both animals and objects are moving. There are intensive free flight studies on the landing response in which insects receive image expansion by their own movement. However, few studies have been conducted regarding how freely flying insects respond to approaching objects. Here, using common laboratory insects for behavioral research, the bumblebee Bombus ignitus, we examined their visual response to an approaching object in the free-flying condition. While the insect was slowly flying in a free-flight arena, an expanding stripe was projected laterally from one side of the arena with a high-speed digital mirror device projector. Rather than turning away reported before, the bumble bees performed complex flight maneuvers. We synchronized flight trajectories, orientations and wing stroke frequencies with projection parameters of temporal resolution in 0.5 ms, and analyzed the instantaneous relationship between visual input and behavioral output. In their complex behavioral responses, we identified the following two visuomotor behaviors: increasing stroke frequency when the bumble bees confront the stripe expansion, and turning towards (not away) the stripe expansion when it is located laterally to the bee. Our results suggested that the response to object expansion is not a simple and reflexive escape but includes object fixation, presumably for subsequent behavioral choice.