Hoverfly visitation in relation to floral colour change (Diptera : Syrphidae)

Flower visitors from several insect taxa (bees, butterflies and some flies) are known to forage assortatively at flowers where floral colour change has occurred; these alterations are often dramatic and the flowers are retained on the plant. Here, a further example of floral colour change is reported and, for the first time, demonstrated how the incidence of such alteration affects foraging in syrphid flies. Feeding behaviour in Rhingia campestris and at least two other hoverfly species is strongly influenced by a striking and extremely localised colour change in the flowers of the wood forget-me-not, Myosotis sylvatica. Nearly 99% of flower visits to pre-change flowers elicited a feeding response whereas only 13 % of visits to post-change flowers led to the same behaviour. Feeding times at post-change flowers were 2-3 times shorter compared to pre-colour-change residence time. Additionally, we confirm centrifugation as a suitable method for extracting low volumes of nectar from small tubular flowers; the change in syrphid feeding behaviour corresponds with both colour change and floral reward status.