Pollinator decline refers to the decrease in the number of insects and other animals that help plants reproduce by moving pollen between flowers. This decline was first noticed in the late 20th century. Many studies show that wild pollinator populations have decreased in regions such as Europe and North America. Similar results from research in South America, China, and Japan suggest that pollinator numbers may be dropping worldwide. Most studies focus on bees, especially honeybees and bumblebees, with fewer studies looking at hoverflies and butterflies.

For domesticated pollinators, such as honeybees kept by humans, the situation is less clear. Between 1985 and 2005, the number of managed honeybee colonies in Europe dropped by 25%, and in North America, it fell by 59% between 1947 and 2005. However, global honeybee numbers increased because of large hive expansions in countries like China and Argentina. Despite this growth, the demand for pollination services for crops that rely on animals tripled while the number of hives only rose by 45%, showing the risks of depending heavily on managed pollinators.

Pollinators help plants reproduce by moving pollen between flowers, which is necessary for some plant species and important for the genetic diversity of others. Since plants are the main food source for many animals, the loss of pollinators has been described by some journalists as an "Armageddon," meaning a very serious threat to ecosystems.

Evidence

Over the twentieth century, the number and variety of insect pollinators have decreased in highly industrialized areas, such as northwestern Europe and eastern North America.

Colony collapse disorder has drawn public interest. A 2013 blog reported that bee hive losses during winter had increased in Europe and the United States, with up to 50% of hives failing.

A 2017 German study, which analyzed 1,500 samples from 63 locations, found that the total weight of flying insects in the area had dropped by 75% over the past 25 years. A 2009 study noted that bee populations had grown by 45% over the last 50 years, while the amount of crops that rely on bees had increased by 300%. The study mentioned no proof that this change caused problems but suggested it might lead to "future pollination problems."

In models showing how plants and their pollinators are connected, these networks can often function well even under tough conditions. However, when conditions become extremely harsh, the entire network may fail all at once.

A 2021 study called the "first long-term assessment of global bee decline" analyzed GBIF data spanning over a century. It found that the number of bee species worldwide dropped sharply after the 1990s, decreasing by 25% between 2006 and 2015 compared to levels before 1990.

Possible explanations

Pollinator decline is hard to measure, but scientists have suggested several possible causes, such as exposure to diseases, parasites, and pesticides; loss of natural habitats; changes in climate; economic factors; competition between native and non-native species; and genetic changes.

Honey bees are considered invasive in many parts of the world where they were introduced. As their numbers grow, they may reduce the populations of native pollinators. Light pollution has been linked to declines in flying insect populations. A study found that air pollution, like that from vehicles, makes it harder for pollinators such as bees and butterflies to detect flower scents. Pollutants like ozone, hydroxyl, and nitrate radicals quickly combine with scent molecules from flowers, causing them to travel shorter distances. This forces pollinators to search farther to find flowers.

Pollinators may also face greater risks of extinction due to global warming, which changes the timing of species’ seasonal activities. Climate change can cause bees to appear at times when flowering plants are not present.

Consequences

Seven out of the ten most important crops worldwide, based on how much is grown, are pollinated by wind (like maize, rice, and wheat) or grow without needing to be planted by animals (such as banana, sugarcane, potato, beet, and cassava). These crops do not need animal pollinators to produce food. Other crops, like sugar beet, spinach, and onions, pollinate themselves and do not need insects. However, about 87.5% of flowering plant species globally depend on animals for pollination, and 60% of crop species use animal pollinators. This includes most fruits, many vegetables, and also fodder. According to the USDA, 80% of insect pollination for crops in the United States is done by honey bees.

A study examined how 15 plant species that rely on animals for pollination would be affected if pollinators were removed by using domes to block them. It found that most species were not harmed by lower pollinator numbers in terms of seed production, but three species were affected.

If animal pollinators disappeared, total agricultural production in the United States could drop by 3 to 8%, with smaller effects on the variety of crops grown. In Brazil, a 2016 study said the biggest impact of pollinator loss would be a drop in income from high-value crops, harming the agricultural sector most. A 2000 study found that honey bees contributed $14.6 billion in value to U.S. food crops. A 2009 study estimated the global value of 100 pollinator-dependent crops at €153 billion (excluding production costs). Despite predictions of pollinator decline, food production has not decreased, as both animal-pollinated and non-animal-pollinated crops have increased in yield at the same rate during this time.

A 2015 study looked at the nutritional effects of pollinator loss. It examined if four populations in low-income countries might face malnutrition if diets did not change or include supplements, but it concluded this outcome could not be reliably predicted. The study said the impact of pollinator loss on a population depends on local diets, and vitamin A is most likely to become deficient, as it is already lacking in many areas.

Other studies also found vitamin A to be the most dependent on pollinators. A 2015 study modeled the effects of losing all pollinators. In that case, 71 million people in low-income countries would lack enough vitamin A, and 2.2 billion people already consuming less than needed would get even less. Similarly, 173 million people would lack folate, and 1.23 million would get less of it. Global fruit supplies would drop by 22.9%, vegetable supplies by 16.3%, and nuts and seeds by 22.1%. This could lead to 1.42 million more deaths yearly from diseases and 27 million more disability-adjusted life years. If only half of pollinators were lost, 700,000 more deaths and 13.2 million more disability-adjusted life years would occur yearly.

One study found that 70% of the world’s dietary vitamin A comes from crops pollinated by animals, as does 55% of folate. Currently, eating pollinated plants provides only 9%, 20%, and 29% of calcium, fluoride, and iron intake, respectively, with most of these nutrients coming from meat and dairy. Also, 74% of global lipids come from oils of pollinated plants, as do 98% of vitamin C.

Solutions

Several experts have urged the use of the precautionary principle.

Environmental groups are working to protect pollinator diversity in both farmland and natural areas. In 2014, the Obama administration released a fact sheet titled "The Economic Challenge Posed by Declining Pollinator Populations." This document explained that the 2015 budget plan suggested Congress allocate about $50 million to help maintain pollinator habitats. It also proposed doubling the land area in the Conservation Reserve Program dedicated to pollinator health and increasing money for studies to understand the effects of pollinator losses.

International efforts stress the importance of public involvement and awareness about pollinator conservation. People are becoming more concerned about pollinators and their health. In the United States, 18 states have passed laws to address pollinator decline. According to the National Conference of State Legislatures, these laws focus on five areas: raising awareness, conducting research, managing pesticide use, protecting habitats, and regulating beekeeping practices.

A 2021 global study on the reasons for pollinator decline stated that global policies should aim to reduce effects from changes in land use, land management, and pesticide use, as these factors were found to be major causes of pollinator loss in most regions.