Pheromone-mediated mating system in a moth species

Sammanfattning: In a series of studies, carried out in the laboratory and in the field in southern Sweden, I have examined factors influencing the mating behaviour of the turnip moth Agrotis segetum. The reproductive potential of the sexes and the mating behaviour was studied. The reproductive potential of males is greater than that of females. Males are ready to mate every night, while females rarely mate more than once during their lifetime. The females do not have to remate to fertilize their entire egg load. Males remate in a higher frequency if given longer time between the mating occasions. The species do not show any elaborate courtship behaviour of female mate rejection. The individual variation of the female sex pheromone, previously identified to consist of at least four components; Z5-10:OAc, Z5-12:OAc, Z7-12:OAc and Z9-14:OAc, was investigated. The amounts and the ratios of the major sex pheromone components in gland extract contents, as well as in the effluvia, were found to vary extensively between the females. The individual female pheromone emission was also established to correlate with female gland content. The female pheromone signal shows high repeatability, indicating a genetic determination of the female sex pheromone signal. The interference and the male choice between synthetic sex pheromone plumes were examined in field experiments. Pheromone-emitting sources interfere, by having overlapping sampling and attraction ranges. The degree of interference is influenced by the composition and amounts of pheromone emitted, as well as the distance between the sources. The results also indicate that male A. segetum moths differ in their pheromone response windows. The males do not discriminate against aberrant female synthetic sex pheromone signals, as long as the species-specificity of the signal is maintained. Finally, male response polymorphism was investigated. Males were found to differ in their pheromone response thresholds, not in pheromone ratio responses. Male moths with a low response threshold also had morphological correlates. The results support the view that female moths may exert mate choice on males by releasing small pheromone amounts and thus select passively for the best-performing males.