VARIABILITY IN ODOR-MODULATED FLIGHT BY MOTHS

Based on previous studies of odor-modulated flight where track paramet er data was lumped and averaged, the speed and orientation of the moth s' movement along their flight tracks have been said to be controlled to maintain certain ''preferred'' values. The results from our fine-sc aled analysis of this behavior show that none of the track parameters typically measured are held constant. The moths' speed along the fligh t track is modulated substantially and predictably: fastest along the straight legs and slowest around the turns. In addition, about half of the individuals studied progressively reduced the peak speed along th e straight legs as they approached the pheromone source. While most of the track legs between the turns were directed upwind, their orientat ions were widely distributed, indicating no preferred direction. Small fluctuations of orientation along some straight legs suggest correcti ve maneuvers to stabilize flight direction about an internal set point . The visual inputs hypothesized to control steering and speed, transv erse and longitudinal image flow, changed continuously during upwind f light in pheromone, but no regular relationship between them was obser ved. We found that the orientation of the longitudinal body axis and t he direction of thrust (course angle) were only rarely coincident duri ng upwind flight to the odor source, suggesting that moths receive sen sory input which differs quantitatively from that calculated by conven tional methods. Our results strongly suggest that the long-accepted hy pothetical mechanisms of control for this behavior do not operate in t he manner in which they have been proposed.