Honeybee and Crop Pollination

Introduction

Pollination plays a vital role as a regulating ecosystem service in nature. Among the insect pollinators, solitary and social bees provide most pollination in both managed and natural ecosystems. Most of the world’s staple foods, including wheat, corn, and rice reproduce without insect pollination. These crops account for 65% of global food production, still leaving as much as 35% depending on pollinating animals (Klein et al. 2007). In part due to the massive scale and homogeneity of modern agriculture, the majority of crops requiring pollination are dependent on managed pollinators, and especially on managed honeybees (Aizenet al. 2008).

Pollination is an ecosystem service that is key to food security. Pollinators are essential for many fruit and vegetable crops. In agriculture, especially among pollen-limited crops, promoting pollination services is a means of increasing productivity without resorting to expensive agricultural inputs of pesticides or herbicides.

Indeed, pollination services are most likely underpinning productivity in many crops without farmers even recognising it, so long as habitat and alternative pollinator forage are readily available as they often are in small holder farming systems. Increasing dependence on pesticides for pest control is also highly detrimental to beneficial insects such as pollinators, unless planned and undertaken with extreme care.

Pollinators in Natural and Agricultural Ecosystems

Pollinator-plant interactions have been estimated to encompass almost 400,000 species, the precise nature of the relationship between plant and pollinator varies enormously. Although some animals visit flowers for nectar or pollen, not all flower visitors bring about pollination. Effective pollinators often have behavioral and anatomical traits that greatly increase the efficiency and accuracy of pollen delivery (Proctor et al. 1996; Lewinsohn et al. 2006). In general, pollination is a mutually beneficial interaction; pollinating animals receive some form of nutritional “reward” for visitation and pollen delivery. Pollen itself can be a reward, serving as the primary food resource for most larval bees and as an important source of protein for some flies, butterflies, birds, and bats. Other plants provide nectar, oils, resins, fragrances, pheromone precursors, and other resources to induce visitation and pollen delivery (Roulston and Cane 2000).

Honeybees as Pollinators

No other group of insects is of more benefit to humans than bees. More than one-third of the world’s crops require pollination to set seeds and fruits, and most meat and dairy industries rely on bees for pollination of fodder (clover and Lucerne) (Diaset al. 1999).

Crops relying on bee pollination include apple, citrus, tomato, melon, strawberry, apricot, peach, mango, grape, carrot, potato, onion, pumpkin, bean, cucumber, sunflower, various nuts, alfalfa, etc. The annual value of this service is estimated at US$112 billion worldwide (Southwick and Southwick 1992).

Even crops that do not require pollination for harvesting, such as those producing fibre or timber, still require pollination to produce further generations, and crops such as cotton that do not require pollination to produce seeds, provide greater yields when pollinators are available (Allen-Wardellet al. 1998).

Apart from direct benefits derived from honeybees in the form of honey and beeswax, indirect benefits realized by way of increased yields of certain farm crops and forest products due to their pollination services are immense. 

Domesticated species: There are two most important hive species. European honeybee, Apis mellifera L. is a native of old world except tropical Asia and introduced to most parts of the new world. It has a foraging range of 3 km. The Indian hive bee, A. cerana indica F., a native of tropical Asia is prevalent in a wide region with a flight range of 1.5 km. It is even a better pollinator than A. mellifera because of their longer foraging period and many other characters (Sihag and Mishra 1995).

Wild species: Two other species, A. dorsata (rock/giant bee) and A. florea (littlebee) are also native of tropical Asia and efficient pollinators. But these cannot be managed for long time, as they do not live in artificial hives. Their  foraging range is 2.5–4.0 and 1 km, respectively. 

Honeybee species can effectively be utilized for pollination of crops because

• Honeybees are dependent on flowers for pollen and nectar as their food
• The bees possess some morphological adaptations favourable for pollen carry over and transfer
• The honeybees can be kept in the hives and are very easy to be managed
• Due to their polylectic nature, honeybees visit large number of plants, therefore, they can pollinate a wide variety of crops
• Their abundance on the crop can easily be manipulated.
• Honeybees have better communication system for food searching and gathering. When a honeybee forager begins foraging on a plant species, continues to do so until the resource gets exhausted. This behaviour of individual foragers has been termed as floral fidelity or constancy (Wells and Wells 1983; Waser 1986). This is very important for the plant species they visit for the effectivity of pollination.
• Behaviour of honeybees can be manipulated by modifying the reward system of the plant/or nectar and pollen storage in the hive or colony’s unsealed brood.
• Colonies of honeybees can be moved to a place of short pollinators supply
• Due to their habits of making nest in the cavities, these bees can be domesticated in the wooden hives. 

The population of both wild and managed pollinators is declining at alarming rates owing to alteration in their food and nesting habitats, shrinkage in natural ecosystems, i.e. forests and grassland ecosystems, pesticide poisoning, diseases and pests, over-collecting, smuggling and trading in certain rare and endangered species. The focus of beekeeping needs to change from conventional honey production to crop pollination.

Augmenting bees for crop pollination

A crop’s pollinator dependence differs between species, including between crops and crop varieties. Some plants must be cross-pollinated, others do not need pollinators but produce better fruit and seed if pollinated, and a number of them are strictly self-pollinated. Further, plants differ in their pollinator-type requirements; some require specific pollinators while others are pollinated by a variety of visitors, and many are wind pollinated. Effective pollinators of the same crop may vary from one site to another. Specific knowledge on pollinator dependence and types is important for agriculture and biodiversity (including agro-biodiversity) conservation.

One mistake often made by a fruit, vegetable, or seed producer regarding bee pollination is to assume that “the neighbor’s bees” will provide sufficient pollination of his crop. Although honeybees from a single hive will fly 2–3 miles from the colony, the radius of greatest efficiency and greatest pollination is only 200–300 yards from the colony. There are many flowers competing for the bee’s attention; some may be more attractive or “profitable” to work than the crop needing pollination. Bees will not fly a great distance to forage on an unattractive crop.

By moving bees directly into a field, a grower can increase the flight activity in that area. However, there are several considerations one should make, and procedure one should follow.

• Time of placement of honeybee colonies: When 5–10% of the flowering has initiated, honeybee colonies are placed on the crop.
• Site of placement of honeybee colonies: The colonies are placed near the target crops so that they can actively move and bring about cross pollination and less energy is utilized in travelling:
• Method of placement of honeybee colonies: Colonies are placed either in groups or are scattered, and further, either around the target crop or scattered in between as per the convenience of the beekeeper (Abrol., 2011).
• Colony arrangement: Bees are most efficient when closest to the colony; therefore, to achieve the most efficient distribution of foragers, the colonies should be distributed at 300–500 yard intervals. Inexperienced foragers work closer to the hive, then disperse with age and experience. Some crops or specific varieties of some crops are unattractive to bees. In such cases, a solution is to flood the area with bees. Provide water for bees. Honeybee colonies are active throughout the year. Honeybees also are trained to pollinate specific crops. The extracts of flowers the crop to be pollinated is fed to the bees in sugar syrup. The bees get conditioned to the aroma of the crop, visit the flowers thereby effecting pollination. 
• Protecting Bees from Pesticides : Confining bees to the hive by screening the entrance and the top after removal of the inner cover might prevent overheating and minimize losses, as long as there is no direct hit by the insecticide on the open colony.
• Minimum Colony Strength : Each hive, enclosing the colony or swarm of bees, is a family unit and consists of a laying queen, a few drones, and several thousand worker bees. Because the worker bees pollinate crops, it is important to understand how their populations change throughout the seasons. In early spring, a colony may have 10,000–20,000 workers, but by summer the colony should have reached a population of 40,000–60,000 workers. During these months the lower portion of the hive, called the brood chamber, is filled with eggs, larvae, and pupae called brood, which are reared in the cells of the comb. Generally, the larger the brood area, the greater the demand for nectar and pollen, thus the greater foraging activity by the bees. This in turn results in more pollination. Colonies used in pollination rental must have brood, and the amount of brood is a strong indication of the effectiveness of the colony for pollination.

Challenges in Managed Crop Pollination

The fact that the bee pollination enhances crop yields has been established (Abrol 1993). Evidently, bee/insect should be encouraged for increased and sustainable agriculture production. In India, the total cultivated area is about 160 million hectares and at least one third (if not half) of the areas is under entomophilous crops which require insect pollination.

At a very modest rate of 3 colonies per hectare we need 160 million colonies of honeybees but against this requirement we have just less than one million bees colonies at present. This would be possible only if the apiculture as a whole gets boost and number of colonies are multiplied and managed. Besides, it is very necessary to survey different agroclimatic zones to determine the distribution and abundance of pollinating insects so that pollinators specific to different zones are multiplied and managed. Regions with less abundance should be supplemented with apiaries.

Conclusion

Pollination is a service Nature provides that we have tended to take for granted, and that we often do little to encourage until we start to lose it. As wild ecosystems are increasingly converted to more human dominated uses to meet the compelling demands of food security, it is critical for us to understand what pollination services are most important for food security, and how we can preserve pollinator services in sustainable farming systems.

References

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Abrol, DP (2011). Pollination biology: Biodiversity conservation and agricultural production. Springer, New York, USA, p. 85-107.

Aizen M, Garibaldi L, Cunningham S, Klein A (2008). Long-term global trends in crop yield and production reveal no current pollination shortage but increasing pollinator dependency. CurrBiol 18:1572–1575.

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Sihag RC, Mishra RC (1995). Crop pollination and Apiscerana. In: Kevan PG (ed) The Asiatic Hive Bee: Apiculture, Biology and Role in Sustainable Development in Tropical and Subtropical Asia, Enviroquest Ltd., Cambridge, Ontario, (Canada) pp 135–142.

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Content contributors :

• Pratap A. Divekar, Division of Crop Protection, ICAR-Indian Institute of Vegetable Research, Varanasi -22305
• Suresh Nebapure, Division of Entomology, ICAR-Indian Institute of Agricultural Research, New Delhi -110012
• Sujan Majumder, Division of Crop Protection, ICAR-Indian Institute of Vegetable Research, Varanasi -22305
• Chandan Kumar Verma, Division of Crop Protection, ICAR-Indian Institute of Vegetable Research, Varanasi -22305