Fine‐scale structure of odour plumes in relation to insect orientation to distant pheromone and other attractant sources

Abstract

ABSTRACT. This paper describes an experimental method for simulating an odour plume in the field so that its fine‐scale characteristics may be determined. It was found that the ‘odour’ arrived at a series of fixed points up to 15 m from the source in a series of discrete bursts, which were widely distributed in time but were typically 0.1 s long and 0.5 s apart. The strengths of the bursts were also found to be widely distributed and some contained considerable fluctuations. Thus an odour plume is not continuous, but intermittent, and appears at a fixed point downwind of the odour source as a series of bursts of odour which are variable in strength and duration. The distribution of the length of bursts and the time between them does not greatly vary with distance from source. Although concentration does decay with distance from source, instantaneous measurement would not be a reliable guide to the mean concentration and hence to position relative to source. To obtain reliable positional information from the odour plume an insect would have to average received stimuli over many seconds. More information is therefore required about the dynamics of insects' olfactory responses.