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Fig. 1

Diversity of insect pollinators of onion in Himalayas of Uttarakhand, India
Diversity of insect pollinators of onion in Himalayas of Uttarakhand, India

Fig. 2

Insect pollinator density obtained through in-situ method of sampling in onion crop at three time frames of the day during peak flowering period (*F-values calculated at 5% level of significance)
Insect pollinator density obtained through in-situ method of sampling in onion crop at three time frames of the day during peak flowering period (*F-values calculated at 5% level of significance)

Fig. 3

Assessment of per cent fruit set with respect to total number of flowers per umbel under different pollination treatments.
Assessment of per cent fruit set with respect to total number of flowers per umbel under different pollination treatments.

Floral biology of onion composite variety “VL Piaz-3”

Floral Character Details
Time of flower opening From 6.20 h to 17.45 h (Throughout the day)
Anthesis Early morning hours from 6.25 to 7.25 h
Anther dehisces Observed from 7.45 h to 16.45 h
Stigma receptivity High between 9.15 h to 15.15 h (Examined through Hydrogen peroxide method proposed by Zeisler (1933))
Number of flowers per umbel Ranged between 682 to 1211 (842±132.51 average of 25 umbels)
Number of umbels per plant Ranged between 4 to 13 (7.32±2.29 average of 25 plants)
Number of umbels per m2 Ranged between 19–65 (36.66±11.43 average of 12 plots)
Days for umbel formation Ranged between 131–144 days (137.44±3.79 days* average of 100 plants) (19th February to 4th March, 2021)
Days for first flowering Ranged between 143–155 days (149.96±6.54 days* average of 100 plants) (3rd march to 15th March, 2021)
Days for last flowering Ranged between 203–216 days (209.92±3.96 days* average of 100 plants) (2nd May to 15th May, 2021)
Total flowering period of crop Ranged between 60–73 days (67.76±3.83 days* average of 100 plants) (3rd March to 15th May, 2021)
Total flowering period of each umbel Ranged between 13–19 days (15.92±1.98 days average of 25 umbels)

Foraging rate of pollen and nectar foragers of A. c. indica at three time intervals in a day during three flowering periods

Pre peak flowering (<25%) Peak flowering (>50%) Post peak flowering (<25%)
Bee foragers 10.00 h 13.00 h 16.00 h F-value p-value 10.00 h 13.00 h 16.00 h F-value p-value 10.00 h 13.00 h 16.00 h F-value p-value
No. of flowers visited by pollen foragers 24.52±1.91 a 23.52±1.44 b 19.71±1.63 c 1.79* 0.018 31.86±2.72 a 29.86±1.79 a 30.57±2.92 a 0.41 0.863 27.48±6.49 b 28.95±5.53a 25.71±5.82 c 0.14 0.0098
No. of flowers visited by nectar foragers 23.42±2.13 b 26.41±1.57 a 23.54±1.95 b 0.64* 0.0069 16.33±1.98 b 17.69±2.01 b 19.11±1.38 a 1.65* 0.021 26.14±1.63 ab 27.18±1.25a 24.69±1.87 c 0.36* 0.0089
No. of umbels visited by pollen foragers 4.95±1.28a 4.19±0.94c 4.57±1.10b 3.68* 0.0261 3.24±0.74a 3.60±1.01a 3.45±1.03a 1.31* 0.32 4.14±0.79b 4.71±1.31a 4.19±1.03b 5.06* 0.0083
No. of visited by nectar foragers 3.98±1.01b 3.87±0.69c 4.23±0.98a 0.42* 0.0085 2.13±0.47c 3.01±0.57a 2.94±0.73b 0.67* 0.0099 4.23±1.03b 3.99±1.07c 4.57±0.87a 0.89 0.0053

Time spent in seconds by individual pollen and nectar forager bee of A. c. indica on onion flowers during three time frames and three flowering periods

Pre peak flowering (<25%) Peak flowering (>50%) Post peak flowering (<25%)
Bee foragers 10.00 h 13.00 h 16.00 h F-value p-value 10.00 h 13.00 h 16.00 h F-value p-value 10.00 h 13.00 h 16.00 h F-value p-value
Pollen foragers 1.76±0.26 a 1.82±0.51 a 1.80±0.36a 1.91* 0.16 1.47±0.28a 1.34±0.31b 1.44±0.50a 0.80* 0.0058 1.79±0.4a 3 1.78±0.42a 1.77±0.45a 1.30* 0.32
Nectar foragers 3.04±0.61c 3.12±0.70b 3.30±0.62a 11.75* 0.0002 3.46±0.60b 3.28±0.62c 3.92±0.54a 2.57* 0.0077 2.96±0.63b 2.87±0.62c 3.08±0.62a 1.53* 0.0025

Pollen and nectar foragers of A. c. indica visiting onion flowers at three time intervals in 1 m2 area in a span of one minute during three flowering periods (averages from 3 flowering days)

Pre peak flowering (<25%) Peak flowering (>50%) Post peak flowering (<25%)
Bee foragers 10.00 h 13.00 h 16.00 h F-value p-value 10.00 h 13.00 h 16.00 h F-value p-value 10.00 h 13.00 h 16.00 h F-value p-value
Number of pollen foragers 21.29±3.99 c 27.00±5.29b 30.71±5.99a 0.27* 0.0094 19.29±2.81c 39.00±7.90b 42.57±6.55a 1.72* 0.002 26.00±3.65c 43.43±4.79b 46.43±4.12a 1.96* 0.0014
Number of nectar foragers 78.71±3.99a 73.00±5.29b 67.86±3.34 c 0.69* 0.0006 80.71±2.81a 61.43±6.97b 57.43±6.55c 1.77* 0.0018 74.00±3.65a 56.57±4.79b 53.57±4.12c 0.87* 0.0048

Entomophily and artificial pollination methods followed for pollinating onion flowers

Treatments Procedure of pollination Treatments
T1- Indian bee (Apis cerana indica) One individual bee, actively foraging in onion fields was collected through a test tube and released on to a pre-marked umbel and bagged with plastic mesh of 500 micron diameters to prevent escape. One bee per umbel was released every day from initiation of flowering up to seed set. Duration of release 1 hour
T2- European bee (Apis mellifera)
T3- Himalayan bumble bee (Bombus haemorrhoidalis)
T4- Hand gloves (Cloth) The pollens were collected from un-bagged umbel through the cloth hand gloves and gently rubbed over the bagged umbel and covered with plastic mesh after pollination. Umbels were gently rubbed for 3 minutes
T5- Hand gloves (Rubber) The pollens were collected from un-bagged umbel through the rubber hand gloves and gently rubbed over the bagged umbel and covered with plastic mesh after pollination. Umbels were gently rubbed for 3 minutes
T6- Sponge puff The pollens were collected from un-bagged umbel through the puff and gently rubbed over the bagged umbel and covered with plastic mesh after pollination. Umbels were gently rubbed for 3 minutes
T7- Camel Brush The pollens were collected from un-bagged umbel through the camel brush and gently sprinkled over the bagged umbel and covered with plastic mesh after pollination. Pollens were sprinkled for 3 minutes
T8- Control (Open) The umbels were not covered and allowed for free cross pollination by all the pollinating agents
T9- Control (Close) The umbels were covered with plastic mesh and only self-pollination was allowed

Quantitative seed yield data of onion obtained through entomophily and artificial pollination methods

Treatments Fruit set (in %) Average number of seeds per umbel Seed weight per Umbel (in grams) Test weight of seeds (in grams) Yield per ha (in kg)
A. c. indica 46.79 394±6.35b 1.38±0.18b 4.2±0.01b 503.70
A. mellifera 36.46 307±9.02c 1.05±0.22c 3.9±0.02c 383.25
B. haemorrhodalis 21.26 179±4.36d 0.82±0.11d 2.8±0.02d 299.30
Hand gloves (cloth) 11.40 96±3.00f 0.38±0.11g 3.3±0.02e 138.70
Hand gloves (rubber) 8.79 74±3.61g 0.34±0.09h 2.9±0.03g 124.10
Sponge puff 17.34 146±4.73e 0.66±0.19e 3.1±0.02f 240.90
Camel brush 17.10 144±4.58e 0.59±0.15f 2.6±0.01h 215.35
Control (open) 85.99 724±7.00a 3.90±0.47a 4.7±0.01a 1423.50
Control (close) 7.84 66±4.04h 0.31±0.04i 2.2±0.01i 113.15

SE(m) 12.98 0.215 0.013
C.V. 3.141 64.95 6.913
F-values 2461.78* 27.41* 38.67*
p-values 0.00014 0.00007 0.000011

List of insects visiting onion flowers under Himalayan conditions of Uttarakhand, India

Order of insect flower visitors List of insects visiting onion flowers
Hymenoptera (19 species) Apis cerana indica, Apis mellifera, Apis dorsata, Apis florea, Bombus haemorrhoidalis, Vespa tropica, Vespula vulgaris, Andrena hilaris, Megachile rotundata, Osmia inermis, Nomia incerta., Halictus sexcinctus, Ceratina smaragdula, Trigona iridipennis, Xylocopa latipes, Sceliphron curvatum, Megascolia azurea, Ceratina sutepensis, Lithurgus atratus
Lepidoptera (17 species) Celastrina argiolus, Chilades pandava, Danaus chrysippus, Pieris brassicae, Parantica aglea, Euploea core, Aglais caschmirensis, Vanessa cardui, Junonia lemonias, Papillio demoleus, Colias ladakensis, Helicoverpa armigera, Lymantria dispar, Acherontia styx, Pieris rapae, Chilades parrhasius, Danaus genetua
Diptera (14 species) Episyrphus balteatus, Metasyrphus corollae, Eupeodes luniger, Eristalis tenax, Macronomia spp., Calliphora vomitoria, Lucilia cuprina, Musca domestica, Eristalinus quinquelineatus, Sarcophaga carnaria, Helophilus trivittatus, Liosarcophaga dux, Eristalis horticola, Eristalinus megacephalus
Coleoptera (5 species) Oxycetonia versicolor, Clinteria kluge, Chiloba acuta, Heterorrhina elegans, Rhomborrhina spp.
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Life Sciences, Zoology, other