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] 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]

Increasing public awareness[edit]

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.[9]

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.[7]

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.[citation needed]

The disappearance of honeybees was documented in the 2009 film Vanishing of the Bees by George Langworthy and Maryam Henein.[11]

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,[12] 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]

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.[13]

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. [14]

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.[13] 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.[15]

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[16] and may even lead to strong indirect facilitation between pollinators when conditions are harsh.[17] 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.[17]

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.[17]


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.

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. Pages 142–148
  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 d 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. ^ a b 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. ^ Bradshaw, Peter (9 October 2009). "Vanishing of the Bees". The Guardian. Retrieved 22 June 2015. 
  12. ^ Gill, Victoria (7 June 2012) Honeybee virus: Varroa mite spreads lethal disease BBC Nature News, Retrieved 11 June 2012
  13. ^ 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
  14. ^ http://www.eurekalert.org/pub_releases/2008-04/uov-ffd041008.php
  15. ^ 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. 
  16. ^ 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. 
  17. ^ 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) : [2]
  • 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. [3]
  • 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: [4]
  • 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, [5]
  • Xerces Society Pollinator Conservation Program 2006 (North America) [6]
  • 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 [7]
  • 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 [8]
  • Brazilian Pollinators Initiative, Vera Lucia Imperatriz Fonseca; Braulio Ferreira Souza Dias [9] accessed March 2004 THE SAO PAULO DECLARATION ON POLLINATORS [10]
  • The Pollination Home Page [11] US; accessed Jul 2006
  • The North America Pollinator Protection Campaign [12] Coevolution Institute US; accessed Jul 2006
  • Pollinator Conservation Handbook Xerces Society 2005, [13]
  • The Bumblebee Conservation Trust [14] 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.