Pollination ecology of Helicteres isora Linn. (Sterculiaceae)

The flowers of Helicteres isora are large, bisexual and zygomorphic with ro bust corolla. The elongated staminal column is adnate to the gynophore and the ten anthers are grouped at the tip of this column. The ovary with a sho rt style ending in a simple stigma projects beyond the anthers and stays in an erect position. The flowers open daily at 0300-0330 h and are visited b y birds and insects during daytime. The flowers characteristically change t heir colour, being bluish-grey on day one (d(1)), changing to light red on day two (d(2)) and dark red on day three (d(3)). Birds collect nectar more frequently from d(2) and d(3) flowers. Bees collect nectar and pollen mostl y from d(1) flowers. The flowers are not apomictic, but compatible for auto -, geitono- and xenogamy. The bees Ceratina and Trigona mediate autogamy an d geitonogamy by remaining mostly on the same flower while Pseudapis and Am egilla promote xenogamy by their frequent inter-tree movement. The birds qu aker babbler Alcippe poioicephala and Indian myna Acridotheres tristis larg ely promote xenogamy because stigma receptivity continues up to the second day of flower life. Since the two bird species implicated in pollination ar e not entirely nectarivorous, total dependence on them for pollination may not be an ideal strategy, and receiving pollen-collecting bees may help in the reproduction of H. isora. Floral damage caused by the red-vented bulbul , Pycnonotus cafer and by the blister beetle and the insect larvae is detri mental to H. isora reproduction. Natural fruit production is very low which may be due to the in-adequancy of pollinators.