Diversity,abundance and foraging behaviour of insect pollinators in Radish (Raphanus raphanistrum subsp. sativus L.)

Insect pollinators and flowering plants have co-evolved together for millions of years, developing a wide array of mutualistic interactions. Several cultivated plant species depend exclusively on insect-mediated pollination services for their subsistence, reproduction and survival. Radish, Raphanus raphanistrum subsp. sativus, a popular edible root vegetable (Family: Brassicaceae) completely depends on pollinators as self-pollination is totally absent due to sporophytic self-incompatibility. The present study was conducted at the experimental fields of the ICAR-Indian Institute of Horticultural Research, Bengaluru, to understand the diversity and foraging behaviour of insect pollinators in R. sativus. Continuous survey during the flowering period revealed that a total of fifteen insect species that belong to three insect orders (Hymenoptera, Diptera and Lepidoptera) were found to visit R. sativus flowers. The most abundant species was Apis florea L., followed by Apis dorsata F., Tetragonula iridipennis (Smith), Apis cerana F., Lassioglossum sp. and Ischiodon scutellaris F. Floral visitors differed significantly in terms of their visitation frequency, with A. florea (0.76 ± 0.22 visits/flower/ min) being the most frequent visitor followed by A. dorsata (0.66 ± 0.21 visits/flower/ min) and T. iridipennis (0.59 ± 0.14 visits/flower/30 min). The maximum visitation rate was recorded for A. dorsata (7.8 ± 1.40 flowers visited/min) followed by A. cerana (6 ± 1.15). The maximum stay time on individual flower was recorded for Lassioglossum sp. (48.2 ± 3.67 sec) followed by T. iridipennis (44.2 ± 4.24 sec). The maximum numbers of pollen grains were deposited by A. dorsata (206.70 ± 56.45) followed by A. cerana (151.20 ± 31.84). All the floral visitors except A. florea made contact with stigma on every single visit (100 %). While, only 53 per cent of total visitation by the Apis florea led to stigma contact. Further, nectar robbing behaviour was majorly exhibited by A. florea and Delta conoideum compared to all other insect pollinators observed. Based on the overall pollinator effectiveness per day A. dorsata was found to be the most effective single pollinator species.