In flower-animal interactions, floral scent repells florivores and attracts pollinators. For sexually divided plants (e.g., dioecious plants), males and females interact differently with florivores and pollinators, and sexual difference in floral scent has been reported in over half of species studied. However, due to the luck of studies, we can not determine whether the sexual difference in floral scent is based on pollinator or florivore type. In particular, compared with bee pollination systems, fly pollination systems have been less studied. For fly pollination systems, flowers often emit bad smells (e.g., dimethyl trisulfide), and these may attract flies that use decaying organic matters as breeding sites. In this study, we approach the questions 1) whether there is a sexual difference in floral scent in a fly pollination system, 2) whether floral scents are associated with amount of flower visitors including pollinators and florivores. For this survey, we used Eurya japonica, a dioecious shrub in East Asia. We collected floral scent from male and female branches which were then analyzed by GC-MS. To examine how many flower visitors visit shrubs, we then set sticky traps around 20 shrubs and 4 poles (as control).
Results/Conclusions
Eleven chemical components from flowers were detected. These components included bad smells (e.g., dimethyl trisulfide), and terpenes that repells some insects. The components and their amount did not differ significantly between sexes. Among collected arthropods, the abundance of some families in Diptera, Hymenoptera, and Coleoptera on shrubs were significantly greater than those on controls. Among these insects (6873 individuals), most abundant were Diptera (97.9%: Chironomidae 32.5%, Calliophoridae 32.3%, Sciaridae 19.3%, others 13.8%). The abundance of dipteran families present was not positively related with the amount of chemicals. However, four compounds were negatively related with the number of a few dipteran families (i.e., Chironomidae, Empididae, Sciaridae). Our results suggest that primary pollinators do not positively respond to the amount of floral scent. A previous study showed that Calliphoridae (i.e., one of the important pollinators) responded to the existence of dimethil trisulfide, but in our study it did not respond significantly. In fly pollination systems, only existence of chemicals may be needed to attract pollinators and this may be the reason why there is no sexual difference in floral scent of E. japonica.