Circadian Rhythms in Moth Sex Pheromone Communication
Sammanfattning: Sex pheromone communication and related physiological processes are regulated by circadian clock mechanisms in many moth species. This thesis includes studies of circadian rhythms in sexually relevant behaviours and communication in the Egyptian cotton leafworm Spodoptera littoralis, the turnip moth Agrotis segetum, the Indian meal moth Plodia interpunctella and the Mediterranean flour moth Ephestia kuehniella. In females, the daily rhythms in calling behaviour in S. littoralis and E. kuehniella showed persistence in constant dim light, indicating regulation by an internal clock mechanism. In males, the daily peak in pheromone response in S. littoralis was persistent for at least one day in constant darkness. Also male locomotor activity, which we interpret as mate search, was shown to be persistent in a constant environment in E. kuehniella, P. interpunctella and S. littoralis. The peaks in male locomotor activity occurred at approximately the same hours of the day as female calling behaviour. Female calling behaviour and male response to the female sex pheromone were both affected by brief exposures to extract of sex pheromone glands in S. littoralis. These tests indicate that males may use sex pheromone to synchronise their sexual activity with females. A comparative study of E. kuehiella and P. interpunctella showed interspecific differences in circadian behaviours, which are discussed from the perspective of efficient mate finding. E. kuehniella females call at dawn in a light:dark cycle, while the behaviour is persistent in constant darkness and suppressed in constant light. In the related P. interpunctella, females call at dusk and turn arrhythmic in both constant darkness and constant light. Since the two species, as well as several other species of Pyralidae, share the same main pheromone component, we suggest that temporal separation of calling activity has evolved to prevent costly interspecific attraction. We also show immunostainings of PBAN, PDH and corazonin in the brain of both species, indicating spatial differences in expression of at least the two latter neuropeptides. A study of PBAN-like (Pheromone Biosynthesis Activating Neuropeptide) immunoreactivity in the hemolymph of A. segetum showed a circadian rhythm in females. We therefore propose that the previously shown circadian rhythm in pheromone biosynthesis in A. segetum is regulated by gated release of PBAN from the corpora cardiaca. This is further supported by immunostaining for both PBAN and clock protein Period in the corpora cardiaca of A. segetum.
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