role of pollinators in seed production

Pollination is one of the most important mechanisms in themaintenance and promotion of biodiversity and, in general, life onEarth. Many ecosystems, including many agro-ecosystems, dependon pollinator diversity to maintain overall biological diversity.Pollinators strongly influence ecological relationships, ecosystemconservation and stability, genetic variation in the plant community,floral diversity, specialization and evolution. Pollination also benefits society by increasing food security andimproving livelihoods. Pollinators are extremely diverse, with more than 20,000pollinating bee species and numerous other insect and vertebratepollinators.

Introduction

The transfer of pollen from the anthers of aflower to the stigma of the same flower or ofanother flower.

Pollination:

SELF POLLINATED

CROPS

CROSS POLLINATED

CROPS

Self-pollinated crop species occupying less than 15%

The remaining cross-pollinated crops need help of pollinating agents, wind, water or insects for fertilization.

Several essential inputs such as improved seeds, improved implements,irrigation ,fertilizers and pesticides are being used for improvingthe productivity but these components even when fully exploitedmay not give marginal returns if the desired level of pollination isnot achieved.

Pollination and fertilization are the important events in seeddevelopment and maturation (Ragini and Vanangamudi,2006).

Deployment of insect pollinators is considered as one of thecheapest and eco-friendly approaches in maximizing the yield ofcross pollinated crops (Free, 1970). Though butterflies ,moths,beetles ,thrips ,birds play a role in pollination ,Honey bees are theideal pollinators.

An animal that moves pollen from the anthersto the stigmas of flowers, thus effectingpollination. Animals that are known to be goodpollinators of flowers include bees, butterflies,hummingbirds, moths, some flies, some wasps, andnectar feeding bats.

Pollinators:

Beetle PollinationThe least specialized flowers are members of subclass Magnoliidae. These are often pollinated by beetles, although beetles also visit a wide variety of flat flowers (or flat inflorescences that function as single flowers). Some general features of beetle flowers are:Time: Either day or nightStructure: Actinomorphic, numerous floral parts; large bowl shaped, ovules protectedColor: Dull, white, few visual attractions, no nectar guidesScent: Strong, fruity or aminoid; no nectar, food primarily pollen or food bodies

Carrion & Dung Beetles & FliesTime: Either day or nightStructure: Actinomorphic, deep corolla tube with appendages forming trapsColor: Purple, brown (like meat), no nectar guides or nectarScent: Strong, like rotting meat .

Value of pollinators

Animals pollinate approximately 75 percent of the crop plants grownworldwide for food, fiber, beverages, condiments, spices, and medicines.

It has been calculated that one out of every three to four mouthfuls offood we eat and beverages we drink is delivered to us by pollinators.As such, agricultural products that are produced with the help ofpollinators make a significant contribution to the economy.For example, it has been estimated that insect-pollinated crops directlycontributed $20 billion to the United States economy in the year 2000. They also perform key roles in natural ecosystem. By helping to keep plantcommunities healthy and able to reproduce naturally, native pollinators assistplants in providing food and cover for wildlife, preventing erosion, andkeeping waterways clean.Pollinated plants produce fruit and seeds which are a major part of the dietof approximately 25 percent NRCS of bird species, as well as many mammals. Excessive use and improper application of many pesticides impactpollinators and their habitats. Some insecticides directly kill pollinators,particularly pollinating insects, and herbicides reduce forage plant diversityby killing wildflowers.

Legumes Beans, Cowpea, Lima Beans, Lupines, Mung Bean/Green or Golden Gram, Soybean

Vegetables Asparagus, Beet, Broccoli, Brussels Sprouts, Carrot,Cauliflower, Celery, Cucumber, Eggplant, Endive, GreenPepper, Leek, Lettuce, Okra, Onion, Parsnip, Pumpkin,Radish, Rutabaga, Squash, Tomato, Turnip, White Gourd

Fruits, berries and nuts Almonds, Apple, Apricot, Avocado, Blackberry, Blueberry,Cacao, Cashew, Cherry, Chestnut, and nuts ,Citrus,Coffee, Coconut, Date, Fig, Gooseberry, Grapes, Guava,Huckleberry, Kiwi, Kolanut, Litchi, Macadamia, Mango,Olive, Papaw, Papaya,Passionfruit, Peach, Pear,Persimmon, Plum, Pomegranate, Raspberry, Strawberry,Tung, Vanilla, Watermelon

Crops dependent upon or benefited by insect pollination

Oils, seeds and grains Alfalfa, Buckwheat, Canola, Flax, Oil Palm, Safflower, Sesame, Sunflower

Clover and relatives Arrow leaf Clover, Ball Clover, Berseem Clover, Black Medic/Yellow Trefoil, Cider Milkvetch, Crimson Clover, Lespedeza, Peanut, Persian Clover, Red Clover, Rose Clover, Strawberry Clover, Subterranean Clover, Sweet Clover, Trefoil, Vetch, White Clover

Other &ornamental crops

Cotton, Kenaf &Cosmos, shoe flower, Golden rod, Cup & saucer, Tacoma stans, zinnia, coral creeper (Antigonon leptopus), rose, rangooncreeper, aster, wild rose (kuja), hydrangea, violet, portulaca, poinsettia, honey suckle, corn flower, coreopsis, dandelion etc.

Honey bee pollinating crops

APPLE SUNFLOWER CITRUS

COFFEEPUMPKIN

CHILLI

Almond garden Clover crop

Blueberries TOMATO

SQUASH RADISH

Cosmos HibiscusGolden rod

AsterTecoma stans

Zinnia

Edward roseCoral creeper

Rangoon creeper

Ridge gourdCarrot

cotton Pumpkin

Cucumber

Water melon Radish

Rapeseed flower

LucernePigeon pea

Sunflower Niger

17

Pollinated crops

pollinated by Bats

moth

BEE FLORA AND POLLINATION OF CROPS

Bee visits plants for its food, nectar and pollen. This floralfidelity of bees is due to their preference for nectars havingsugar contents and pollens with higher nutritive values. Besidesgetting food for the bees as a result of their visit pollinate anumber of crops.

Qualities of honeybees which make them good pollinators

Body covered with hairs and has structural adaptation for carrying nectar and pollen.Bees do not injure the plantsAdult and larva feed on nectar and pollen which is available in plentyConsidered as superior pollinators, since store pollen and nectar for future useNo diapauses is observed and needs pollen throughout the yearBody size and proboscis length is very much suitable for many cropsPollinate wide variety of cropsForage in extreme weather conditions also

Yield increase due to bee pollination

Crop Per cent yield increase

MustardSunflowerCottonLucerneOnionApple

4332-4817-191129344

Scope of beekeeping for pollination in India: Total area of bee dependant crops in India is around 50 million hectare. One hundred and fifty million colonies are needed to meet this, at the rate of 3 colonies per hectare. In India at present, there are only 1.2 million colonies exist. Hence there is a wide scope for expansion of bee keeping for pollination in India.

Management of bees for pollination

Place hives very near the field source to save bee's energy.

Migrate colonies near field at 10 per cent flowering.

Place colonies at 3/ha for Italian bee and 5/ha for Indian honey bee.

The colonies should have 5 to 6 frame strength of bees, with sealed brood and young mated queen.

Allow sufficient space for pollen and honey storage

Usually a honeybee can visit between 50-1000 flowers in onetrip, which takes between 30 minutes to four hours. In Europe, abee can make between seven and 14 trips a day. A colony with25,000 forager bees, each making 10 trips a day, is able topollinate 250 million flowers.

Pollination by bees - case studies with selected crops

Sunflower Alfalfa or Lucerne

1. Sunflower: It is a cross-pollinated crop. The pollen of the plantcannot fertilize ovary of same plant. Pollen source should be fromdifferent plant. Hence, honey bees acts as important agents forpollination in sunflower. In sunflower, yield increases even up to 600per cent due to bee pollination. It improves quality and quantity ofseeds. Oil content also increases by 6.5 per cent in seeds. To achievethis it requires five strong C. indica colonies or three A. melliferacolonies. Mostly irrigated crop is preferred by bees.

2. Cucurbitaceous vegetables: Cucurbits are monoecious withstaminate and pistil late flowers in same plant. Due to bee pollinationfruit set increases up to 30 to 100 per cent.

3. Alfalfa or Lucerne: These plants have tubular flowers with 5petals joined at base. They posses one large standard petal, 2 smallerpetals on sides and 2 keel petals holding staminal column. When beesits on a keel petal, stamina column strikes against standard petalresulting in shattering of pollen. This is called tripping. Seed setoccurs only if bee sits to trips the flowers.

4. Coriander: In coriander yield increases up to 187 per cent due topollination.

5. Cardamom: It is an important commercial crop depending on beesfor pollination. Here yield increases up to 21 to 37 per cent.6. Gingelly: Another oilseed crop where bee pollination causes 25 percent increase in yield.7. Apple: In apple seed set occurs only if it is pollinated by bees.Fruit is formed only around the seeds. If improper seed set occursfruit shape is lopsided resulting in decreased market value.

It is now apparent that most of the pulses and oilseeds, fruits andorchard crops including vegetables heavily depend on bees for theirpollination.

This is also true for seed production of vegetables like onion,cabbage, cauliflower, tobacco, sun hemp, Alfa Alfa and clovers.The number of colonies of honeybees required per hectare verymuch depends on the strength of foraging bees in the colony, thecrops and prevailing weather conditions.

The optimum number of colonies of average strength may rangefrom 3 to 9 colonies per hectare, since the bees usually foragewithin a radius of about 1 to 2 km to harvest their nectar andpollen loads, and then return to their own hive.

Important features of flower which aid in Honey bee pollination

Colour of the flower

Structure of the flower

Good quality nectar

High concentration of sugars in flowers

Production of Abundant pollen

Honey bee species involved in pollination

• Apis mellifera( European bee)• Apis cerana indica(Indian bee)• Apis dorsata (Rock bee)• Apis florea (Little bee)• Trigona irridepennis (stingless bee)

Rock bee Indian bee

Little bee

Stingless bees

European bee

Apis mellifera is generally preferred

Adoptability

Easy handling

Slow swarming

Tolerance to human management

Honey making habit increases pollination

Factors which influences pollination efficiency

• A biotic factors

Rainfall

Temperature:16OC - 41OC

Wind velocity: Below 15 miles/hr

(Ragini and Vanangamudi,2006)

• Honey bee spp. Body size with hairs

Rock bee

Pollen carrying ability

Little bee

• Hives placement

• Stage of hive placement in the field

• Colony size: 8-10 combs of bees/hive, with more number of broods

•Other agronomic practices-Increases nectar production

Timely application of fertilizers Irrigation (Especially during flowering)

Estimates of increased seed set due to pollinators have been made in different parts of the world

• 22-100% -Radish• 100-300%-cabbage• 100-125%-turnip• 91-135%-carrot• 345-500%-onion

Gingras et al.,1999

Recommendation of bee hives in various important crops

CropNo. of hives per hectare

References

Alfalfa 2.5-8 Williams et al.,1995

Crucifer 2.5 Mayer (1986)

Rapeseed 2.5-15 Scott-Dupree et al.,(1995)

Cucumis melo 2.5 Scott-Dupree et al .,(1995)

Carrot 5 Mayer and lunden (1983)

Cotton 2.5-5 Levin (1986)

Cucumber 10 Williams(1994)

Onion 10-25 Mayer et al., (1993)

Soybean 1-1.5 Sheppard et al.,(1995)

Gourds 2.5-5 Skinner(1987)

Sunflower 4 Williams (1994)

Water melon 5 Williams (1994)

Radish 5 Mayer and lunden (1983)

Attractiveness of the cropNumber of wild beesNumber of competing weeds

Strength and location of bee hivesWeatherGrowers experience

Role of Pollinators

It increases yield in terms of seed yield and fruit yield in many crops.It improves quality of fruits and seedsBee pollination increases oil content of seeds in sunflower.Bee pollination is a must in some self incompatible crops for seed set.Cross-pollination of Lucerne is vital to ensure that the maximumquantity and quality of seed is achieved. Cross-pollination is said to contribute about 89% of the seedyield.Wild pollinators visiting crops can increase the effectiveness ofpollination, and thus the yields and quality of crop production. Profiles of practices that can affect the diversity andabundance of wild pollinators visiting crops give options forfarmers and land managers to promote wild pollinators atdifferent scales of management.

Bee pollination not only results in a higher number of fruits, berriesor seeds, it may also give a better quality of produce, and theefficient pollination of flowers may also serve to protect the cropsagainst pests.The better weight due to sufficient pollination arises from thedevelopment of all seeds in a fruit.

An apple, for example, will only develop all the seeds inside if it hasbeen pollinated by several bees and fully fertilized.

Parameter Bee pollinationSelf

pollinationPer cent increase in bee pollination over selfing

Fruit set (%) 81.00 56.55 24.45

Siliqua length (cm)

13.213±2.140 6.832±0.911 91.93

No. of seeds/pod 8.163±1.923 4.816±1.201 78.84

Seed weight per 100 seeds (g)

1.500±0.316 0.9000±.260 66.67

Table 1. Role of insect pollination in seed production of Radish.

Priti et al.., 2001

Both the quantitative and qualitative characters were expressed better in case of insect pollinated flowers, due to frequent visits of the insect pollinators,

Table 2. Effect of honey bee pollination on seed yield & quality of Radish.

TreatmentSiliqua

/plant

Siliqua/length

(cm)

Grain

/siliqua

Yield/plant

(g)100-seed weight(g)

Germination (%)

Caged with

honey bees

Mean80.62 5.50 2.02 1.25 0.87 76.80

SD 30.67 0.24 0.25 0.54 0.08 17.94

Open

pollination

Mean84.92 5.48 4.30 3.67 1.06 91.00

SD 24.11 0.31 0.64 1.47 0.10 5.81

% increase in open

over cage- - 112.87 193.63 21.83 -

Kapila et al.,2002

Both the quantitative and qualitative characters were expressed better in case of open pollination due to frequent visits of the insect pollinators.

TreatmentsNumber of Seeds set

per pod

A.mellifera 11.571

A.cerena 9.143

A.florea 6.857

CD (P=0.05) 1.896

Table 3.Pollinating efficiency of Apis Species in hybrid seed production of Brassica napus L.

Jasvir Singh et al., 2002

Increased amount of pollen deposition on stigma by A.mellifera because of its large body size with more hairs

Table 4. Relative efficiency of various agents as pollination facilitators in Lucerne.

Increase in the yield was due to combined effect of cross pollination and reduced ovule abortion ,because tripping mechanism carried efficiently by honey bees.

Decrease in the yield in other treatments may be due the absence of tripper and pollen carrier, damage to florets, stigmatic membrane might not have got ruptured. Padmavathi et al., 2003

Treatment Pollination efficiency

(%)

% increase over control

Yield(q/ha)

Test weight

(g)

Germination(%)

Plots caged with abee colony 87.41 119.56 5.55 3.27 91.33

Plots caged without bees 30.37 -91.53 0.59 1.60 45.35

Open pollination 39.81 - 2.52 2.80 88Selfing 1.17 -97.06 0.15 1.58 40.66Hand tripping 15.00 -62.32 1.60 2.48 -walking 34.00 -14.59 2.46 - -Rope pulling 35.95 -9.96 2.42 - -

Table 5. Honey bee pollination requirement for triploid watermelon.

Honey bee visitation treatment

Fruit set% Fruit no per plot Fruit wt(kg)/ per plot

No visits control 0* 0.0* 0.0*2 visits 9* 1.8* 5.5*4visits 25* 5.0* 32.0*8 visits 38* 7.5* 46.9*

16 visits 53* 10.5* 68.8*Open pollinated

control(about 24 visits)

80* 16.0 106.1

Alan walters, 2005

Maximum fruit set and development was recorded in open pollination compared to other treatments .Since triploid watermelon do not provide sufficient viable pollen to fertilize pistillate flowers, it requires more number of visits.

Pumpkin cultivarFruit/ha Total weight

Average fruitweight(kg)

Without bees

BeesWithout

beesBees

Without bees

Bees

Appalachian 4,765 5,955 26,242 44,755 5.5 7.6Autumn king 4,595 4,765 27,260 35,363 5.9 7.5Gold rush 3,233 4,085 23,712 33,846 7.4 8.3Motherlode 3,803 4,425 22,930 33,781 6.1 7.7Aspern 5,105 4,340 27,198 30,134 5.4 7.0Gold strike 3,148 3,998 20,136 28,754 6.4 7.3Howden 2,638 3,403 14,888 24,394 5.7 7.2Ichabod 3,148 2,893 16,454 21,347 5.3 7.4Mean 3,805 4,233 22,353 31,547 5.9 7.5

Table 6. Effect of honey bee pollination on pumpkin (Cucurbita pepo) fruit yield.

Alan Walters and Bradely, 2006

Pumpkin cultivar

Seeds/Pumpkin Seed weight(g)/pumpkinSeed weight/100

seed (g)

Without bees Bees Without

bees Bees Without bees Bees

Mother Lode 551 700 78.4 106.4 14.8 15.7

Autumn king 644 684 86.8 100.8 13.7 15.1

Ichabod 555 633 64.4 103.6 10.9 16.8

Gold stike 531 609 75.6 86.8 14.3 14.3

Gold Rush 553 595 81.2 81.2 14.8 13.7

Appalachain 506 595 70.0 89.6 13.7 15.7

Aspen 503 590 78.4 109.2 15.4 18.8

Howden 591 570 78.4 86.8 13.4 15.7

Mean 554 622 75.6 95.2 13.7 15.7

Table 7. Effect of honey bee pollination on pumpkin (Cucurbita pepo) seed yield.

It is due to increased pollen deposition on the stigma and high pollinator density with maximum pollination activity

Conclusion

On a global level, the Convention on BiologicalDiversity has identified the importance ofpollinators . It is apparent that speculativeand practical utilization of heterosis in termsof seed yield and quality are directly relatedto the role of insects principally bees in crosspollinated crops which exhibits male sterilityand self incompatibility mechanism . Thus aneffective pollination through careful planningand skillful management strategies inentomophilous cross pollinated crops can beachieved if strong bee hives are maintained inthe apiaries beside tumbling pesticideapplication which are detrimental to honeybees.

pollinators are increasing in seed yield alsoincreasing total food production in thecountry.

Honeybees are the “ Angles of agriculture “, the farmers bestfriend . Using honey bees for crop production, the production can beincreased manifolds , however it needs to be encouraged amongfarmers.

REFERENCES

Bees and their role in forest livelihoods research paper .EncyclopediaGoogle scholarVegetable seed production text book