Studies on Floral Traits and Pollinator Foraging Behaviour in Onion {Allium cepa F.)

摘要

Insect pollination services play a major role in onion. Allium cepa L. due to the prevalence of protandry. A study was conducted at the experimental fields of ICAR - Indian Institute of Horticultural Research, Bengaluru, Karnataka, India (13.13 °N; 77.49 °E) to understand the foraging behaviour of major insect pollinators associated with onion crop (cv. Arka Kalyan). Continuous surveillance revealed that onion took 70 - 75 days for flower bud initiation and 90 - 95 days for maximum flower opening.A single bulb produced 4.00 ± 1.05 flowering stalks which produced umbel inflorescence that consisted of numerous individual flowers called florets. The mean number of florets in an umbel (449.30 ± 29.47) and the duration of each floret (5.60 ± 0.52 days) were worked out. In general, each floret produced 6.00 -7.00 anthers (Mean ± SE: 6.10 ± 0.32) with a mean number of 1581 pollen grains per anther. A total of 1735 and 1852 individual pollinators were observed visiting the onion during 2020 and 2021, respectively. The floral visitor’s data from transect sampling revealed their abundance as : Apis florea > Trigona iridipenuis > Apis dorsata > Apis cerana > Ischiodon scutellaris > Eristalis obliquus for two consecutive years. Of all floral visitors, A. florea had recorded highest visits (26.92 ), while Eristalis obliquus recorded the least foraging visits (7.38 ). The observations on foraging behaviour revealed that major foraging activity was carried out by A. cerana, as it spent maximum amountof time on inflorescence (3.30 ± 0.82 umbel / min) followed by A. dorsata (2.50 ±0.71 umbel / min) and the least with T. iridipennis (1.40 ± 0.52 umbel / min). However, time spent / umbel was maximum with T. iridipenuis (45.80 ± 4.41 sec / umbel) and the least was found with A. cerana (16.10 ± 1.85 sec/ umbel).