MICRO-FORAGING ROUTES OF BICOLLETES-PAMPEANA (COLLETIDAE) AND BEE-INDUCED POLLEN PRESENTATION IN CAJOPHORA-ARECHAVALETAE (LOASACEAE)

In flowers of Cajophora arechavaletae Urb. the stamens are hidden from flower visitors in naviculate petals. In the male phase the stamens s uccessively migrate at irregular intervals to the centre of the flower where they present pollen. Therefore, non-specialised pollinators can not predict the time of pollen presentation. The oligolectic females o f Bicolletes pampeana are effective pollinators of Cajophora arechaval etae. Females and males can elicit stamen movements by pressing the sc ales of the nectaries outwards with their head while taking up nectar. If this stimulus is responded to, up to 3 stamens move and reach the centre of the flower on average after 2.4 min. Experiments showed that the stimulus of nectar scale pressing was responded to maximally when the inter-stimulus interval was at least 14 min. B. pampeana females have evolved a foraging strategy which is adapted to the unique pollen presentation of C. arechavalete flowers. On microforaging routes they trapline 30-60 flowers and, therefore, most frequently come back to t he same flower after intervals of about 3 min. This is exactly the per iod after which a female can expect pollen in the centre of the flower if her previous stimulus was responded to. Competition between the fe males causes them to return to the flowers at such short intervals.