The role of male pheromones of a moth ( Y. padellus ) in sexual behaviour.

1. Aletta C. Bakker, Peter Roessingh and Steph B. J. Menken UvA, IBED, Kruislaan 320, 1098 SM Amsterdam, The Netherlands, abakker@science.uva.nl The role of male pheromones of a moth (Y. padellus) in sexual behaviour. Introduction Little is known about the function of pheromones of male moths. Male pheromones are generally believed to function as aphrodisiacs that play a role during courtship behaviour. However actual evidence for their mode of action is scarce. In some cases, males form a lek and use pheromones to attract females over long distances. Male pheromones can serve as a signal for both sexes. We believe that male pheromones are potentially important signals for assortative mating and sexual selection. In this poster we present methods and results on the study of sexual behaviour, female choice and the function of the male pheromone of a moth Yponomeuta padellus. Evidence for pheromone production in Yponomeuta males. Many male moths have structures called hairpencils. It is believed that the large surface of such structures facilitate the diffusion of volatiles like male pheromones. Analysis through SEM and videotape observations of Yponomeuta padellus males supported the presence and use of these hairpencils during sexual behaviour. Yponomeuta males also exhibit wingfanning behaviour which could further facilitate pheromone dispersal. SEM photo of abdomen tip of male with hairpencil (6) extended. Photo from video of male that fully protruded his two hairpencils (arrow). Attraction of males to female pheromone and females to male pheromone in a y-tube. We used an y-tube olfactometer to study the response of females to the male pheromone. First we performed a control experiment to confirm male attraction to female pheromones in our set-up. We observed a significant response of males towards synthetic female pheromone when clean air was the alternative (n=20; p=0.012 Binomial Test). Subsequently we tested female response to the odours of male moths exposed to synthetic female pheromone when the single synthetic pheromone was the alternative. We found no significant effect (n= 32; p>0.05 Binomial Test). A control experiment showed no effects of the synthetic female pheromone on the behaviour or choice of females. Preliminary conclusion: females do not show a preference for male pheromone in a simple y-tube test. Assortative mating or not? In experiment 1 females from two host plants (Prunus and Crataegus) were offered a choice between two males (brothers) raised on either of these two host plant. Females preferentially mated with the male from the same host plant (assortative mating). In experiment 2 we used non related males (as what would be expected in the field). This showed however no such preference of the females. The experiments should be repeated using moths from one population and identical set-up conditions before we can draw any conclusions. Male investment: sperm transfer. There is a significant difference in weight change between the mated (n=13) and unmated (n=11) individuals; p<0.001. The Pearsons correlation between weight change of females and males is –0.72 (p=0.003). Our results show that males loose 13.5% (S.E.=0.5%) of their body weight when they mate compared to 2.3% (S.E.=0.2%) natural weight loss when they do not mate. Conclusion: Males do invest! It has to be tested what the composition of the spermatophore is in apyrene and eupyrene sperm and whether a nuptial gift is involved. What we want to do next: Sperm transfer: is sperm transfer the same for the first, second, third etc. mating of the male? Female choice: do females prefer a virgin male over a male that has already mated? Do females prefer an unrelated male over a related male? Sexual behaviour: Analyses of importance of wingfanning and behavioural patterns for mating success (Theme, Noldus B.V.). Chemical compounds of the male pheromone: Testing new methods for non-invasive sampling (solid phase micro extraction) and using GC-MS for identification of male pheromone compounds. Acknowledgments: Louis Lie (culture of Yponomeuta), Maarten Hilbrant (SEM, photo hairpencils) Jacco Jong (y-tube experiments) and Marieke de Boer & Paulien de Bruijn (assortative mating experiment 1).