Vertical Stratification and Directionality as Determinant of Plant- Pollinator Interactions in Sweet Orange (Citrus sinensis L. Osbeck)

A total of 18 species of insect visitors were observed to visit the sweet orange( Citrus sinensis L. Osbeck) flowers. Among the pollinators the Hymenoptera constituted major group of insects followed by Diptera and Lepidoptera. 18 species of insects belonging to 3 orders, 9 families and 13 genera were honeybees Apis florea F., Apis cerana, Apis dorsata F., Apis mellifera L., Carpenter bees Xylocopa fenestrata, X. pubescens. Besides, Musca spp., Eristalis spp., Syrphid spp., and butterflies were other insect visitors observed on citrus flowers. Of all these insects, honeybees were most abundant and comprised more than 63% of the flower visitors. Insect visitors were found to behave differently to different in Inflorescence height. It was interesting to note that honeybees visited more middle branches than the upper or lower ones whereas carpenter bees collected nectar and pollen mostly from the upper branches. The dipteran insects including Musca spp., Syrphus spp. and small Hymenopteran insects like Nomia and Lasioglossum spp. referred to as ‘others’ mostly visited lower branches. The impact of direction of plant had a pronounced effect on abundance of foraging population. Generally, more population was observed in east and west compared to north and west directions. Population of bees were at par in north and south directions. The results revealed that stratification and directionality had a significance influence on the behaviour of flower visiting insects.