Pollinator decline

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The term pollinator decline refers to the reduction in abundance of insect and other animal pollinators in many ecosystems worldwide beginning at the end of the twentieth century, and continuing into the present day.

Pollinators participate in sexual reproduction of many plants, by ensuring cross-pollination, essential for some species, or a major factor in ensuring genetic diversity for others. Since plants are the primary food source for animals, the reduction of one of the primary pollination agents, or even their possible disappearance, has raised concern, and the conservation of pollinators has become part of biodiversity conservation efforts.


The value of bee pollination in human nutrition and food for wildlife is immense and difficult to quantify.

60 to 80% of the world’s flowering plant species are animal pollinated,[1] and 35% of crop production[1] and 60% of crop plant species[2][full citation needed] depend on animal pollinators. It is commonly said that about one third of human nutrition is due to bee pollination. This includes the majority of fruits, many vegetables (or their seed crop) and secondary effects from legumes such as alfalfa and clover fed to livestock.[citation needed]

In 2000, Drs. Roger Morse and Nicholas Calderone of Cornell University, attempted to quantify the effects of just one pollinator, the Western honey bee, on only US food crops. Their calculations came up with a figure of US $14.6 billion in food crop value.[3] In 2009, another study calculated the worldwide value of pollination to agriculture. They calculated the costs using the proportion of each of 100 crops that need pollinators that would not be produced in case insect pollinators disappeared completely. The economic value of insect pollination was then of €153 billion.[4]

There has not been sufficient study to quantify the effects of pollinator decline on wild plants and wild life that depend on them for feed. Some plants on the endangered species list are endangered because they have lost their normal, native pollinators.[citation needed] Honey bees are not native to the Western Hemisphere. The role of honey bees in the Western Hemisphere is almost exclusively agricultural.[citation needed]

Increasing public awareness[edit]

The steady increase in beekeeper migration (for pollination service on agricultural crops) has masked the issue of pollinator decline from much public awareness, however sudden blocks to such migration could have catastrophic results on the global food supply.[citation needed]

There are international initiatives (e.g. the International Pollinator Initiative (IPI)) that highlight the need for public participation and awareness of pollinator, such as bees, conservation [5]

Possible explanations[edit]

Pesticide misuse[edit]

Studies have linked neonicotinoid pesticide exposure to bee health decline.[6][7] These studies add to a growing body of scientific literature and strengthen the case for removing pesticides toxic to bees from the market. Pesticides interfere with honey bee brains,[6] affecting their ability to navigate. Pesticides prevent bumble bees from collecting enough food to produce new queens.[7]

Neonicitinoids are highly toxic to a range of insects, including honey bees and other pollinators.[8] They are taken up by a plant’s vascular system and expressed through pollen, nectar and guttation droplets from which bees forage and drink. They are particularly dangerous because, in addition to being acutely toxic in high doses, they also result in serious sub-lethal effects when insects are exposed to chronic low doses, as they are through pollen and water droplets laced with the chemical as well as dust that is released into the air when coated seeds are planted. These effects cause significant problems for the health of individual honey bees as well as the overall health of honey bee colonies and they include disruptions in mobility, navigation, feeding behavior, foraging activity, memory and learning, and overall hive activity.

A widely-cited French 2012 study of Apis mellifera (western honey bee or European honey bee)[9] that focused on the neonicotinoid pesticide thiamethoxam, which is metabolized by bees into clothianidin, a pesticide cited in legal action, tested the hypothesis that a sub-lethal exposure to a neonicotinoid indirectly increases hive death rate through homing failure in foraging honey bees. When exposed to sub-lethal doses of thiamethoxam, at levels present in the environment, honey bees were less likely to return to the hive after foraging than control bees that were tracked with Radio-Frequency Identification (RFID) tagging technology, but not intentionally dosed with pesticides. Higher risks are observed when the homing task is more challenging. The survival rate is even lower when exposed bees are placed in foraging areas with which they are less familiar.

In their 2014 study of Bombus terrestris (buff-tailed bumblebee or large earth bumblebee), published in Functional Ecology researchers tracked bees using RFID tagging technology, found that a sub-lethal exposure to either a neonicotinoid (imidacloprid) and/or a pyrethroid (?-cyhalothrin) over a four-week period caused an impairment of the bumble bee's ability to forage.[10]

Another study examined the impacts of the pesticide imidacloprid on bumble bee colony health.[7] Researchers exposed colonies of the bumble bees to levels of imidacloprid that are realistic in the natural environment, then allowed them to develop naturally under field conditions. Treated colonies had a significantly reduced growth rate and suffered an 85% reduction in production of new queens compared to unexposed control colonies. The study is particularly noteworthy because it shows that bumble bees, which are wild pollinators, are suffering similar impacts of pesticide exposure to “managed” honey bees. Wild pollinators provide essential services both in agriculture and to a wide range of wild plants that could not survive without insect pollination.

On March 21, 2012, commercial beekeepers and environmental organizations filed an emergency legal petition with the U.S. Environmental Protection Agency (EPA) to suspend use of clothianidin, urging the agency to adopt safeguards. The legal petition is supported by over one million citizen petition signatures, targets the pesticide for its harmful impacts on honey bees. The legal petition points to the fact that the EPA failed to follow its own regulations. EPA granted a conditional, or temporary, registration to clothianidin in 2003 without a required field study establishing that the pesticide would have no “unreasonable adverse effects” on pollinators. Granting conditional registration was contingent upon the subsequent submission of an acceptable field study, but this requirement has not been met. EPA continues to allow the use of clothianidin nine years after acknowledging that it had an insufficient legal basis for initially allowing its use. Additionally, the product labels on pesticides containing clothianidin are inadequate to prevent excessive damage to non-target organisms, which is a second violation of the requirements for using a pesticide and further warrants removing all such mislabeled pesticides from use.

It is a label violation to apply most insecticides on crops during bloom, or to allow the pesticide to drift to blooming weeds that bees are visiting. Yet such applications are frequently done, with little enforcement of the bee protection directions.[citation needed] Pesticide misuse has driven beekeepers out of business, but can affect native wild bees even more, because they have no human to move or protect them.[citation needed]

Bumblebee populations are in jeopardy in cotton-growing areas, since they are dosed repeatedly when pesticide applicators apply insecticides on blooming cotton fields while the bees are foraging.[citation needed]

Widespread aerial applications for mosquitoes, med-flies, grasshoppers, gypsy moths and other insects leave no islands of safety where wild insect pollinators can reproduce and repopulate. One such program can reduce or endanger pollinator populations for several years.[citation needed]

Many homeowners feel that dandelions and clover are weeds, that lawns should only be grass, and that they should be highly treated with pesticides.[citation needed] This makes a hostile environment for bees, butterflies and other pollinators.[citation needed]

See also:

Rapid transfer of parasites and diseases of pollinator species around the world[edit]

Increased international commerce within modern times has moved diseases such as American foulbrood and chalkbrood, and parasites such as varroa mites,[11] acarina mites, and the small African hive beetle to new areas of the world, causing much loss of bees in the areas where they do not have much resistance to these pests. Imported fire ants have decimated ground nesting bees in wide areas of the southern US.

Loss of habitat and forage[edit]

The push to remove hedgerows and other "unproductive" land in some farm areas removes habitat and homes for wild bees. Large tractor mounted rotary mowers may make farms and roadsides look neater, but they remove bee habitat at the same time. Old crops such as sweet clover and buckwheat, which were very good for bees have been disappearing. Urban and suburban development pave or build over former areas of pollinator habitat.

Clear cut logging, especially when mixed forests are replaced by uniform age pine planting, causes serious loss of pollinators, by removing hardwood bloom that feeds bees early in the season, and by removing hollow trees used by feral honey bees, and dead stubs used by many solitary bees.

Bees and other pollinators faced increased risk of extinction because global warming causes their natural habitats to move whereas the bees are not always be able to move to these new areas.[12]

Nectar corridors[edit]

Migratory pollinators require a continuous supply of nectar sources to gain their energy requirements for the migration. In some areas development or agriculture has disrupted and broken up these traditional corridors, and the pollinators have to find alternative routes or discontinue migration. A good example is the endangered lesser long-nosed bat (Leptonycteris curasoae) which was formerly the main pollinator of a number of cactus species in southwestern United States. Its numbers have severely declined, in part due to disruption of the nectar corridors that it formerly followed. Other migratory pollinators include monarch butterflies and some hummingbirds.

Hive destruction[edit]

Bees are often viewed negatively by homeowners and other property owners. A search for "carpenter bees" on the Internet primarily yields information on removal rather than information regarding bees in a positive light. Recent hysteria regarding [Africanized bee|killer bees] has contributed to these views.[citation needed] Beekeepers find increased vandalism of their hives, more difficulty in finding locations for bee yards, and more people inclined to sue the local beekeeper if they are stung, even if it is by a yellow jacket.[citation needed]

Light pollution[edit]

See also: Light pollution

Increasing use of outside artificial lights, which interfere with the navigational ability of many moth species, and is suspected of interference with migratory birds may also impact pollination. Moths are important pollinators of night blooming flowers and moth disorientation may reduce or eliminate the plants ability to reproduce, thus leading to long term ecological effects.[citation needed] This is a new field and this environmental issue needs further study.

Threat by invasive honey bees[edit]

Many native pollinators decline in population when faced with competition from invasive honey bees. For example, the western honey bee is invasive in the United States, the wild population consisting entirely of feral bees escaped from European bee colonies imported to fertilize non-native, old-world crops. Where colony collapse disorder reduced invasive honey bee populations in the US, native pollinators sometimes have made recoveries[citation needed], restored to their natural niche by the loss.

Air pollution[edit]

Researchers at the University of Virginia have discovered that air pollution from automobiles and power plants has been inhibiting the ability of pollinators such as bees and butterflies to find the fragrances of flowers. Pollutants such as ozone, hydroxyl, and nitrate radicals bond quickly with volatile scent molecules of flowers, which consequently travel shorter distances intact. There results a vicious cycle in which pollinators travel increasingly longer distances to find flowers providing them nectar, and flowers receive inadequate pollination to reproduce and diversify. [2]

Changes in seasonal behaviour due to global warming[edit]

In 2014 the Intergovernmental Panel on Climate Change reported that bees, butterflies and other pollinators faced increased risk of extinction because of global warming due alterations in the seasonal behaviour of species.[12] Climate change was causing bees to emerge at different times in the year when flowering plants were not available.

The structure of plant-pollinator networks[edit]

Wild pollinators often visit a large number of plant species and plants are visited by a large number of pollinator species. All these relations together form a network of interactions between plants and pollinators. Surprising similarities were found in the structure of networks consisting out of the interactions between plants and pollinators. This structure was found to be similar in very different ecosystems on different continents, consisting of entirely different species.[13]

The structure of plant-pollinator networks may have large consequences for the way in which pollinator communities respond to increasingly harsh conditions. Mathematical models, examining the consequences of this network structure for the stability of pollinator communities suggest that the specific way in which plant-pollinator networks are organized minimizes competition between pollinators[14] and may even lead to strong indirect facilitation between pollinators when conditions are harsh.[15] This makes that pollinator species together can survive under harsh conditions. But it also means that pollinator species collapse simultaneously when conditions pass a critical point. This simultaneous collapse occurs, because pollinator species depend on each other when surviving under difficult conditions.[15]

Such a community-wide collapse, involving many pollinator species, can occur suddenly when increasingly harsh conditions pass a critical point and recovery from such a collapse might not be easy. The improvement in conditions needed for pollinators to recover, could be substantially larger than the improvement needed to return to conditions at which the pollinator community collapsed.[15]


The decline of pollinators is compensated to some extent by beekeepers becoming migratory, following the bloom northward in the spring from southern wintering locations. Migration may be for traditional honey crops, but increasingly is for contract pollination to supply the needs for growers of crops that require it.

Conservation and restoration efforts[edit]

Efforts are being made to sustain pollinator diversity in agro and natural eco-systems by some environmental groups. Prairie restoration, establishment of wildlife preserves, and encouragement of diverse wildlife landscaping rather than mono culture lawns, are examples of ways to help pollinators.

Use of alternative pollinators[edit]

Honey bees are usually the most widely chosen insects in most managed pollination situations. However they are not the most efficient pollinators of some flowers. Alternative pollinators, such as for example, leaf cutter and alkali bees in alfalfa pollination and bumblebees in greenhouses for tomatoes are used to augment and in some cases replace honey bees. A wide variety of other bees can be found in the environment that are specialist pollinators (some only using one plant species). However, most of these alternative insects' value as pollinators and their relationships with plants are as yet little known.

In the US, some think that other pollinators will in time replace the lost honey bees, blamed on introduced acarine and varroa mites, but general pollinator decline was already happening before these entered the picture. Only in a few areas are wild populations of pollinators building up; in most areas they are declining as quickly as honey bees.[citation needed]

Furthermore, pollinators cannot be exchanged on a one-for-one basis, as various species of bees pollinate in different ways. Bees may deliberately collect pollen, but have different collection techniques, which can greatly affect their efficiency as pollinators.

Flowers are frequently specifically adapted to one pollinator, or a small group of pollinators because of floral structure, color, odor, nectar guides, etc. Proposed alternative pollinators may not be physically capable of accomplishing pollination, or they may not be attracted to the flower of that plant species, or they may rob nectar by cutting sepals, thus avoiding pollination. Understanding the pollination needs of a species is vital to understanding of a plant species, yet this is often poorly understood. In horticulture it is critical to the economic success of the grower, and crops have sometimes been abandoned from general use in an area because of lack of understanding of pollinator needs.[citation needed]

See also[edit]


  1. ^ a b Kremen, C.; Williams, N.M.; Aizen, M.A.; Gemmill-Herren, B.; LeBuhn, G.; Minckley, R.; Packer, L.; Potts, S.G.; Roulston, T.a.; Steffan-Dewenter, I.; Vázquez, D.P.; Winfree, R.; Adams, L.; Crone, E.E.; Greenleaf, S.S.; Keitt, T.H.; Klein, A.-M.; Regetz, J.; Ricketts, T.H. (2007). "Pollination and other ecosystem services produced by mobile organisms: a conceptual framework for the effects of land-use change". Ecology Letters 10 (4): 299–314. doi:10.1111/j.1461-0248.2007.01018.x. PMID 17355569. 
  2. ^ Roubik, D.W., 1995. Pollination of Cultivated Plants in the Tropics. In: Agricultural Services Bulletin 118. Food Agriculture Organization of the United Nations, Rome, Italy.
  3. ^ The Value of Honey Bees As Pollinators of U.S. Crops in 2000, Drs. Roger Morse and Nicholas Calderone of Cornell University (2000) : [1]
  4. ^ Gallai, N., Salles, J. M., Settele, J., & Vaissière, B. E. (2009). Economic valuation of the vulnerability of world agriculture confronted with pollinator decline. Ecological Economics, 68(3), 810-821
  5. ^ Byrne, A., and Fitzpatrick, U. 2009. Bee conservation policy at the global, regional and national levels. Apidologie 40(3):194-210
  6. ^ a b Henry, Mickaël; Maxime Béguin, Fabrice Requier, Orianne Rollin, Jean-François Odoux, Pierrick Aupinel, Jean Aptel, Sylvie Tchamitchian, and Axel Decourtye (April 20, 2012). "A Common Pesticide Decreases Foraging Success and Survival in Honey Bees". Science 335 (6076): 348–350. doi:10.1126/science.335.6076.1555. 
  7. ^ a b c Whitehorn, Penelope; Dave Goulson (April 2012). "Neonicotinoid Pesticide Reduces Bumble Bee Colony Growth and Queen Production". Science 336 (6076): 351–352. doi:10.1126/science.1215025. PMID 22461500. 
  8. ^ Feldman, Jay. "Protecting Pollinators: Stopping the Demise of Bees" (PDF). Pesticides and You. Beyond Pesticides. 
  9. ^ Henry, Mickaël; Béguin, Maxime; Requier, Fabrice; Rollin, Orianne; Odoux, Jean-François; Aupine, Pierrick; Aptel1, Jean; Tchamitchian, Sylvie; Decourtye, Axel (20 April 2012). "A Common Pesticide Decreases Foraging Success and Survival in Honey Bees" (PDF). Science 336 (6079): 348–350. doi:10.1126/science.1215039. PMID 22461498. Retrieved 4 October 2014. 
  10. ^ Gill, Richard J.; Raine, Nigel E. (7 July 2014). "Chronic impairment of bumblebee natural foraging behaviour induced by sublethal pesticide exposure". Functional Ecology 28 (6): 1459–1471. doi:10.1111/1365-2435.12292. 
  11. ^ Gill, Victoria (7 June 2012) Honeybee virus: Varroa mite spreads lethal disease BBC Nature News, Retrieved 11 June 2012
  12. ^ a b Gosden Emily (29 March 2014) Bees and the crops they pollinate are at risk from climate change, IPCC report to warn The Daily Telegraph, Retrieved 30 March 2014
  13. ^ Bascompte, J.; Jordano, P.; Melián, C. J.; Olesen, J. M. (2003). "The nested assembly of plant–animal mutualistic networks". Proceedings of the National Academy of Sciences 100 (16): 9383–9387. doi:10.1073/pnas.1633576100. 
  14. ^ Bastolla, U.; Fortuna, M. A.; Pascual-García, A.; Ferrera, A.; Luque, B.; Bascompte, J. (2009). "The architecture of mutualistic networks minimizes competition and increases biodiversity". Nature 458 (7241): 1018–1020. doi:10.1038/nature07950. 
  15. ^ a b c Lever, J. J.; Nes, E. H.; Scheffer, M.; Bascompte, J. (2014). "The sudden collapse of pollinator communities". Ecology Letters 17 (3): 350–359. doi:10.1111/ele.12236. 


  • The Value of Honey Bees As Pollinators of U.S. Crops in 2000, Drs. Roger Morse and Nicholas Calderone of Cornell University (2000) : [3]
  • The Forgotten Pollinators by Drs. Stephen L. Buchmann and Gary Paul Nabhan is a classic work describing the pollinator crisis. In the vein of Rachel Carson, their opening chapter, "Silent Spring and Fruitless Falls" describes the risk in a nutshell. They go on to illustrate the problem and propose some solutions.
  • Pollination, the Forgotten Agricultural Input, Dr. Malcolm Sanford of the University of Florida, published in Proceedings of the Florida Agricultural Conference and Trade Show, Lakeland, FL, September 29–30, 1998, J. Ferguson, et al. eds., pp. 45–47. [4]
  • Biological Diversity: Pollinators Science in Africa, Issue 2, Sun Jul 30 2006 United Nations Food and Agriculture Organization position paper on the subject of pollinator decline: [5]
  • The International Initiative for the Conservation and Sustainable use of Pollinators: A proposal for a plan of action Convention on biological diversity, Montreal, 12–16 November 2001, [6]
  • Xerces Society Pollinator Conservation Program 2006 (North America) [7]
  • POLLINATOR BIODIVERSITY A CO-ORDINATED GLOBAL APPROACH, Eardley, C. 2001. Acta Hort. (ISHS) 561:331-332(FAO) VIII International Symposium on Pollination; Pollination: Integrator of Crops and Native Plant Systems [8]
  • The Economic Impacts of Pollinator Declines: An Approach to Assessing the Consequences, Peter G. Kevan and Truman P. Phillips, Conservation Ecology v.5, i.1 June 2001 [9]
  • Brazilian Pollinators Initiative, Vera Lucia Imperatriz Fonseca; Braulio Ferreira Souza Dias [10] accessed March 2004 THE SAO PAULO DECLARATION ON POLLINATORS [11]
  • The Pollination Home Page [12] US; accessed Jul 2006
  • The North America Pollinator Protection Campaign [13] Coevolution Institute US; accessed Jul 2006
  • Pollinator Conservation Handbook Xerces Society 2005, [14]
  • The Bumblebee Conservation Trust [15] Great Britain; accessed Jul 2006
  • The impact of aerial fenitrothion spraying upon the population biology of bumble bees (Bombus Latr.: Hym.) in southwestern New Brunswick. Plowright, R.C., B.A. Pendrel and I.A. McLaren. 1978. Canadian Entomology 110: 1145-1156. - A case study in the loss of pollination for blueberries, caused by gypsy moth spraying, which also killed bumblebees
  • Bascompte, J.; Jordano, P.; Melián, C. J.; Olesen, J. M. (2003). "The nested assembly of plant–animal mutualistic networks". Proceedings of the National Academy of Sciences 100 (16): 9383–9387. doi:10.1073/pnas.1633576100. 
  • Bastolla, U.; Fortuna, M. A.; Pascual-García, A.; Ferrera, A.; Luque, B.; Bascompte, J. (2009). "The architecture of mutualistic networks minimizes competition and increases biodiversity". Nature 458 (7241): 1018–1020. doi:10.1038/nature07950. 
  • Lever, J. J.; Nes, E. H.; Scheffer, M.; Bascompte, J. (2014). "The sudden collapse of pollinator communities". Ecology Letters 17 (3): 350–359. doi:10.1111/ele.12236.