How does insect visitation trigger floral colour change?

1. Visitation by the key pollinator, Bombus terrestris , was implicated in inducible flower colour change in Lupinus pilosus . Behaviour at the flower and rate of visitation by these bumble bees had specific effects; exclusion of this flower visitor led to retarded onset, and reduced rate, of colour change.2. The foraging behaviour of B. terrestris was influenced by floral colour change in L. pilosus . Choice of pre-change flowers was greater than random in relation to the proportion of colour phases available within the plant population.3. Levels of floral manipulation that mimicked the flower handling characteristics of visiting bumble bees confirmed that triggering of the pollen release mechanism is necessary for the instigation of colour change.4. Moreover, this study suggests that, in L. pilosus , an aspect of pollination (pollen deposition by bees and/or subsequent pollen tube growth within the style) is linked with colour change and may act as the trigger for such change.