Pollinator decline is based on observations made at the end of the twentieth century of the reduction in abundance of pollinators in many ecosystems worldwide.
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 honeybee populations in the US have dropped about 90% in the past 50 years, except for the Southwest where they have been replaced by africanized bees.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 honeybee 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 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 thoughout the year to build up their hive.
The value of bee pollination in human nutrition and food for wildlife is immense and difficult to quantify.
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 honeybee, 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 pollinators.
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.
Bumblebee populations are in very bad shape in cotton-growing areas. Bumbles are hit over and over when pesticide applicators apply insecticides on blooming cotton fields while the bees are foraging.
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 knock down pollinator populations for several years.
The chemlawn philosophy has convinced people 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.
Rapid transfer of parasites and diseases of pollinator species around the world
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. Migratory pollinators, such as monarch butterflies and some hummingbirds depend on nectar corridors for their annual migration, and development or agricultural practices have disrupted some of these vital corridors.
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 honeybees, and dead stubs used by many solitary bees.
If one runs a seach for "carpenter bees" the Internet, one will mostly find information about how to kill these valuable pollinators, not how to encourage and use them. This attitude ("Get the bug spray, ma, I just saw a bee!") is one of the worst problems our pollinators have. The "killer bee" hype has increased this paranoia. 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.
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 alkalai bees in alfalfa pollination and bumblebees in greenhouses for tomatoes are used to augment and in some cases replace honeybees. 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 honeybees, 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 are building up; in most areas they are declining as badly as honeybees.
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) : 
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.
- Many people, even folks in agriculture who should be highly aware of this issue are not. Dr. Malcolm Sanford of the University of Florida has written an important position paper: Pollination, the Forgotten Agricultural Input, which is online at: 
- The United Nations Food and Agruculture Organization has also issued a position paper on the subject of pollinator decline: Biological Diversity: Pollinators 
The International Initiative for the Conservation and Sustainable use of Pollinators: A proposal for a plan of action 
Xerces Society Pollinator Conservation Program (North America) 
POLLINATOR BIODIVERSITY A CO-ORDINATED CLOBAL APPROACH (FAO) 
- Article in Conservation Ecology: The Economic Impacts of Pollinator Declines: An Approach to Assessing the Consequences 
Brazilian Pollinators Initiative 
African Pollinator Initiative 
THE SAO PAULO DECLARATION ON POLLINATORS 
The Pollination Home Page 
The North America Pollinator Protection Campaign 
Pollinator Conservation Handbook