Inhibition of biochemical terpene pathways in <i>Achillea millefolium</i> flowers differently affects the behavior of bumblebees (<i>Bombus terrestris</i>) and flies (<i>Lucilia sericata</i>)

Floral scents serve multiple functions in the interactions with organisms. Flowers of Achillea millefolium (Asteraceae) emit scent bouquets dominated by terpenoids. These flowers are mainly visited by flies and beetles, whereas bumblebees, common visitors at other Asteraceae, are absent from A. millefolium flowers. In order to test how a reduced mono- and sesquiterpenoid emission affect insect behaviour we inhibited the biochemical pathways towards the production of terpenoids of A. millefolium plants and conducted behavioural choice tests. The inhibition resulted in reduced emission rates of most mono- and sesquiterpenes and thus altered the olfactory phenotype of the flowers. In a flight cage, flies usually chose flowers with a natural scent bouquet, bumblebees clearly preferred flowers treated with inhibitors. These findings confirm that floral scents play a pronounced role in foraging decisions of flower visiting insects and support the notion that responses towards scent are animal species-specific emphasising the role of scents as floral filters