THE POLLINATION AND BREEDING SYSTEM OF DIPTEROCARPUS-OBTUSIFOLIUS (DIPTEROCARPACEAE) IN DRY DECIDUOUS FORESTS OF THAILAND

The pollination biology of Dipterocarpus obtusifolius (Teijsm.), an ob ligately insect-pollinated dry deciduous dipterocarp tree, is describe d. For the first time, the pollinators of a Dipterocarpus species are identified, and they are found to be large Lepidoptera, a new pollinat ion syndrome for this tree family. D. obtusifolius produces relatively few large, pink, pendulous flowers that emit a strong fragrance upon opening. Flowers open at dusk and remain open for 24-36h. Nectar secre tion occurs at flower opening and continues through the next day. poll en is maximally available at night but much pollen remains available t o daytime visitors. The stigma is spatially separated from the anthers but pollen presentation and stigma receptivity occur simultaneously. In artificial pollination experiments there was intense selection pres sure, through abscission of young fruit, in favour of outcrossing. Pol lination did not occur in the absence of insect vectors. Large moths ( Sphingidae and Noctuidae) are the primary pollination vectors at night and account for 60% of pollen transfer. Butterflies (primarily Pierid ae and Papilionidae) pollinate flowers during the day. It is likely th at birds pollinate a small proportion of flowers. The pollination synd rome and breeding system of this species is discussed in relation to i ts biogeography.