The partly eaten Acmadenia heterophylla flower is providing pollen, nectar and petals to please its pollinator guest. Sacrifice of petals as insect food is an existential hazard often not avoidable by flowers.
In an ideal world the insects would only consume nectar and pollen, while brushing pollen on and off during visits. The real world is replete with contingencies. Less than perfect or ideal, its surprises are wide-ranging and fun for all who don't mind real.
If some colourful floral parts are left to serve as signposts for visitors until full pollination is achieved, plant and flower goals remain achievable. For losing a petal along the way in life is no sacrifice, as Elton John might sing (Bond and Goldblatt, 1984; iNaturalist; http://pza.sanbi.org).