Flight behaviour of males of two moths, Cadra cautella and Pectinophora gossypiella, in homogeneous clouds of pheromone

Abstract It is thought that orientation by male moths along pheromone plumes is guided by interception of filaments of pheromone along that plume and that clean air gaps are required for upwind progress. Given that several investigations have determined that cells sensitive to pheromone can resolve only low rates of encounter with pheromone filaments, generally up to 10 pulses/s, it would appear that individual filaments encountered at higher rates would not be resolved by the insects' sensory system and therefore the stimulus would be perceived as a non-flickering signal. Behaviourally, this has been thought to be expressed as the cessation of upwind progress. Previous studies with Cadra cautella (Walker) (Lepidoptera: Pyralidae) demonstrated that upwind flight by these males is not inhibited in rapidly pulsed plumes. Therefore, to determine whether a flickering signal is required for upwind progress by C. cautella , males were introduced to homogeneous clouds of pheromone in a wind tunnel and their behaviour recorded. For comparison, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), a species from a long-diverged lineage, was also used. Upwind progress by C. cautella is not impeded by the constant olfactory signal provided by a homogeneous cloud of pheromone, but this is not true for P. gossypiella . Furthermore, although C. cautella directs its flight upwind in a homogeneous cloud, its heading is not always due upwind. Potential mechanisms are discussed. It is suggested that C. cautella does not require a flickering signal to progress upwind.