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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.
Observation of pollinator decline
As plantings have grown larger, the need for concentrated pollinators at bloom time has grown. At the same time populations of many pollinators has been declining, and this decline has become a major environmental issue today. Pollination management seeks to protect, enhance, and augment agricultural pollination.
For example, feral honey bee populations in the US have dropped about 90% in the past 50 years, except for the Southwest where they have been replaced by Africanized bees. At the same time managed honey bee colonies have dropped by about two thirds.
Monoculture needs very high populations at bloom, but can make the area quite barren, or even toxic when the bloom is done.
The study of pollinator decline is also interesting some scientists, as bees have the potential to become a keystone indicator species of environmental degradation. Any changes in their abundance and diversity will influence the abundance and diversity of the prevailing plant species. This is a mutual dependency as bees rely on a steady nectar source and pollen source throughout the year to build up their hive.
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.
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.
There has not been sufficient study to quantify the effects of pollinator decline on wild plants and wild life that depends on them for feed. Some plants on the endangered species list are endangered because they have lost their normal, native pollinators. It is important to recognize that honey bees are not native to the Western Hemisphere, so any loss of honey bees does not represent a threat to native plants; the role of honey bees in the Western Hemisphere is almost exclusively agricultural.
Increasing public awareness
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 US food supply.
Possible explanations for pollinator decline
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. Pesticide misuse has driven beekeepers out of business, but can affect native wild bees even worse, because they have no human to move or protect them.
Widespread aerial applications for mosquitoes, med-flies, grasshoppers, gypsy moths and other insects leaves no islands of safety where wild insect pollinators can reproduce and repopulate. One such program can reduce or endanger pollinator populations for several years.
Many homeowners feel that dandelions and clover are weeds, that lawns should only be grass, and that they should be highly treated with pesticides. This makes a hostile environment for bees, butterflies and other pollinators.
Increased international commerce within modern times has moved diseases such as American foulbrood and chalkbrood, and parasites such as varroa mites, acarine 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.
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.
Clearcut 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.
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.
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 killer bees has contributed to these views. 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.
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. This is a new field and this environmental issue needs further study.
Solutions to pollinator decline
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
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 monoculture lawns, are examples of ways to help pollinators.
Use of alternative pollinators
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, leafcutter 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 badly as honey bees.
Furthermore pollinators cannot be exchanged on a one-for-one basis. They are not all equal. Some are generalists, some are specialists. Some are brawny; some are feeble. Some have long tongues; some short. Some work at colder temperatures than others. 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.
- The Value of Honey Bees As Pollinators of U.S. Crops in 2000, Drs. Roger Morse and Nicholas Calderone of Cornell University (2000) : 
- 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. 
- 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: 
- 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, 
- Xerces Society Pollinator Conservation Program 2006 (North America) 
- 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 
- 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 
- Brazilian Pollinators Initiative, Vera Lucia Imperatriz Fonseca; Braulio Ferreira Souza Dias  accessed March 2004 THE SAO PAULO DECLARATION ON POLLINATORS 
- The Pollination Home Page  US; accessed Jul 2006
- The North America Pollinator Protection Campaign  Coevolution Institute US; accessed Jul 2006
- Pollinator Conservation Handbook Xerces Society 2005, 
- The Bumblebee Conservation Trust  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.