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.

Effects of intermittent and continuous pheromone stimulation on the flight behaviour of the oriental fruit moth, Grapholita molesta

“…successful upwind flight in a plume within the cloud decreases, presumably because peak-to-trough amplitude decreases at the receptor level. Murlis & Jones (1981) have shown that even at between 2 and 15 m from the source the peak concentration of a filament of ionized air (presumed to mimic that of pheromone) is 22 times the mean concentration of the plume and up to 150 times more concentrated than the lowest trough concentrations.…”

Host plant volatiles serve to increase the response of male European grape berry moths, Eupoecilia ambiguella, to their sex pheromone

“…In-Xight arrestment behaviour in response to very high pheromone doses is probably linked to the plume structure and dose. As an odour plume is not continuous but intermittent, upwind Xying males encounter bursts of odour alternating with clean air (Murlis and Jones 1981;Kaissling 1997). The density of such bursts will be higher near the source than farther downwind such that males can encounter concentrations that are overdosed, and, consequently, show in-Xight arrestment behaviour.…”

Variable wind directions and anemotactic strategies of searching for an odour plume

“…However it has been established by atmospheric physicists (Pasquill 1974 is carried away from the source in a relatively straight line for a considerable distance while the plume as a whole may be snaking to and fro across wind. The snake is not the path of the wind: the plume snakes simply because the wind direction varies (Murlis and Jones 1981 ;David et al 1982).…”