Pheromone-controlled anemotaxis in moths

Abstract

Males of several moth species possess very sensitive chemoreceptors for detecting conspecific female sex pheromone. Behavioural experiments conducted in wind tunnels, as well as electrophysiological experiments with pulsed odor stimuli, revealed that moths are remarkably well adapted to the rapid changes in stimulus concentration they encounter in a natural odor plume. As a walking or a flying moth orients to an odor source, it displays turning responses to individual odor pulses of only a few tens of ms duration. Both receptor cells and central neurons can resolve up to ten odor pules per second. When odor pulses stop coming, a walking moth circles on the spot, and a flying moth selects a path transverse to the odor plume, both types of behaviour being thought to serve for regaining olfactory information. Concentration gradients within the odor plume, however, do not provide reliable information on the location of the odor source. The odor pulses rather act to trigger locomotion upwind (positive anemotaxis), a strategy that will eventually guide the male to the odor source. Moths progress upwind most effectively when the odor pulses are repeated at a rate of about 3/s, regardless of the stimulus intensity. The orientational cues by which the animal adjusts its upwind course of locomotion are provided by mechanical and visual stimuli. Possible mechanisms for odorelicited anemotaxis are discussed, in particular the cybernetic model system of Kramer ( 1996) with two feedback loops, that explains anemotactic orientation in flight based solely on the flow of ground patterns over the animal’s eyes. A model system for walking requires only one feedback loop. Computer simulations of anemotactic behaviour produce flight and walking tracks similar to those observed in real animals. The odor stimulus modulates several parameters of this model.