FLY BY NIGHT - Rock bee pollinators of Red Sanders

by S P Rao, J B Atluri, C Subba Reddi and R J S Aluri, India

Pterocarpus santalinus, commonly known as Red Sanders, is small deciduous tree. It grows in Andhra Pradesh, India. We have been studying the reproductive ecology of this economically important tree species in its natural habitat in the Sri Lankamalai Reserve Forest. This is typically dry, hilly and rocky habitat.

The trees have no leaves during February and March. The summer showers trigger the development of new foliage and flowering Pterocarpus santalinus exhibits a very special flowering pattern: during the flowering period, the tree does not have flowers every day. On some days there is mass flowering and this is followed by little or no flowering for 2-5 days. In one tree that was watched continuously, flowering occurred over period of 28 days, with mass blooming on five occasions. The first mass bloom was evident on 18 April, second on 21 April, third on 26 April, fourth on May and fifth on May 1995. Mass blooming on two consecutive days is rare phenomenon. This kind of flowering pattern with few bursts of flowering is energetically advantageous to the plant. It concentrates reproductive energy into those few, specific flowering periods.

The flowers of Red Sanders open at night: flower opening begins around 2330 hours. All the flowers open en masse: despite its name the petals of Red Sanders are in fact bright yellow.

On one occasion, the research team went into the deep forest at 0400 hours and located tree in full bloom. By then, the rock bee Apis dorsata was actively foraging at the flowers of this tree. The foraging activity of the bees continued up to 0630 hours. On another occasion, the research team spent the whole night in the forest to find out the exact time of flower opening. We noticed rock bee visitation at 0230 hours. There was a full moon. First, the bees were found foraging on a nearby tree of Bauhinia racemosa, where they were collecting pollen. The rock bees on Pterocarpus santalinus continued foraging up to 0500 hours and from then onwards their activity declined and had ceased totally by 0730 hours. During daylight hours, no other insect visitor was observed except Xylocopa latipes that made occasional visits.

This is a summary of the full paper presented at India’s National Conference on Tropical Bees and the Environment, see News Around the World