Pollination Biology of Jujubes and Longans and the Importance of Insects in the Pollination of Crops in Vietnam
The floral and pollination biology of jujubes (Ziziphus mauritiana) and longans (Dimocarpus longan) were studied near Hanoi, Vietnam. Jujube is a protandrous species with three phases of flowering. After a brief asexual phase, anthers dehisce and release pollen in the afternoon of the day of anthesis. Stigmas become most receptive the following day when flowers are actively secreting nectar. Both jujube and longan flowers are visited during the day by insects of many families, particularly honeybees and flies (syrphids, calliphorids, and muscids). Honeybees, Apis cerana, made up 84% of floral visitors to jujube flowers and 47 – 95% to longan inflorescences. Bagging experiments revealed that diurnal insect visitors are very important in fruit production of both jujubes and longans. In jujubes, no fruits were set during the first pollination trial early in the flowering period. Fruit set increased to 0.17% midway through flowering and 2.21% for the trial conducted late in the flowering period. Fruit set recorded one week after anthesis suggested that all types of pollination may result in fruits, but 7 weeks after anthesis only open pollination (unbagged flowers) and diurnal pollination treatments yielded fruits. Most fruits (~97%) were estimated to result from honeybee visits to flowers. Longans are also predominantly pollinated by diurnal insects (~84%), but with minor contributions from wind pollination (8.4%) and self-pollination (7.7%). A. cerana was estimated to contribute 67% of longan pollination. Pollination requirements for 39 Vietnamese crops were reviewed. Most benefit from insect pollination. For 8 crops important in Vietnamese agriculture for which there were sufficient data, crop yields and values were estimated. Honeybee pollination resulted in ~50% of yields of these 8 crops, contributing ~900 millionion USD of their total values. This analysis indicates that the pollination service provided by honeybees is enormous.