Pollinator decline: evidence and responses
Are pollinators declining? The evidence, why it matters for crops, drivers from habitat loss to neonicotinoids and Varroa, and what farmers can do.
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Bees, flies, butterflies, moths, beetles, birds and bats carry pollen between flowers. They are essential for the fruit, vegetables, nuts, oilseeds and spices that make diets nutritious. Since the mid-2000s, reports of colony collapse in honey bees, falling wild bee numbers and disappearing butterflies have made "pollinator decline" a global concern. That concern has driven new pesticide rules in Europe, national strategies in many countries, and research programmes worldwide.
What does the evidence actually show, how much do crops depend on pollinators, and what can farmers do?
Why pollinators matter for food
The landmark assessment by IPBES (2016) found that:
- about 75% of the leading global food crop types benefit to some extent from animal pollination;
- these crops make up about 35% of global crop production by volume;
- the annual market value of crops directly affected by pollinators is estimated at US$235–577 billion;
- pollinator-dependent crops supply a large share of dietary vitamins A and C, folate, calcium and other micronutrients.
Dependence varies greatly. Rice, wheat and maize are wind- or self-pollinated and need no animals. Melons, pumpkins, cocoa and kiwifruit would yield little without them. Many crops, such as mustard, sunflower, soybean and coffee, still gain 10–40% in yield and quality from good pollination. In India, pollination matters for mustard, sunflower, cucurbits, apple, litchi, mango, cardamom and many vegetables grown for seed.
Pricing pollination on an apple farm
An orchard in Himachal Pradesh produces apples worth ₹10 lakh a year. Apple is in the "great" dependence class: without pollinators, yields would fall by roughly 40–90%. Taking a midpoint dependence of 0.65, about ₹6.5 lakh of the crop's value can be attributed to pollination. In some apple valleys, a shortage of pollinators, combined with too few pollinizer varieties in the orchard, has led growers to rent honey bee colonies at flowering, often 3–5 colonies per hectare, and sometimes to pollinate by hand.
The evidence for decline
The picture is mixed, and it differs between managed and wild pollinators.
- Managed honey bees: the global number of hives has increased over the past 50 years, driven by beekeeping in Asia, Africa and South America. Some regions report high colony losses, however. US beekeepers have often lost 30–50% of colonies a year since the mid-2000s, replacing them at extra cost.
- Wild pollinators: long-term data from Europe and North America show declines in the range and abundance of many wild bees, bumblebees, hoverflies and butterflies. Several species have been listed as threatened. Global data from the tropics, including India, are much sparser.
- Pollination deficits: field studies show that many crops already yield less than they could because of insufficient pollination, especially in intensively farmed landscapes with little natural habitat.
Drivers
IPBES and later reviews identify several interacting drivers:
- Land use change and habitat loss: conversion of meadows, forests and field margins to large monocultures removes nesting sites and flowers. Mass-flowering crops give only a brief pulse of food.
- Pesticides: insecticides, especially systemic neonicotinoids such as imidacloprid, clothianidin and thiamethoxam, can harm bees at sublethal doses, affecting navigation, foraging and colony growth. The European Union restricted three neonicotinoids in 2013 and banned their outdoor use in 2018. Some fungicides and herbicides also have indirect effects.
- Pests and pathogens: the parasitic mite Varroa destructor, which spread from the Asian honey bee to the European Apis mellifera, and the viruses it transmits, such as deformed wing virus, are major causes of honey bee colony losses. Diseases can also spill over from managed to wild bees.
- Climate change: shifts in flowering time and pollinator activity, heat stress, and range shifts, such as bumblebees disappearing from the southern edges of their ranges.
- Invasive species, including invasive plants and predators such as the Asian hornet in Europe.
The drivers interact. A bee stressed by poor nutrition is more vulnerable to pesticides and disease.
What farmers can do
- Protect bees from pesticides:
- use IPM and spray only when thresholds are crossed;
- avoid spraying crops in flower, or spray in the evening when bees are not foraging;
- choose products with lower bee toxicity;
- warn nearby beekeepers before spraying;
- follow label warnings for systemic seed treatments.
- Provide food and nesting: flower strips, hedgerows, field margins, trees on farms, and diverse rotations that keep flowers available through the season. Bare ground and dead wood help ground-nesting and wood-nesting bees.
- Manage pollination: place bee colonies at flowering, for example 3 colonies per hectare in mustard and 5 or more in apple. Plant pollinizer varieties in orchards. Use stingless bees or bumblebees in protected cultivation.
- Support beekeeping: India's National Beekeeping and Honey Mission (2020) promotes scientific beekeeping with Apis mellifera and the native Apis cerana, honey testing laboratories and pollination services.
Policy responses
- The EU restricted neonicotinoids, adopted a Pollinators Initiative (2018, revised 2023), and includes pollinator recovery targets in its Nature Restoration Law.
- National pollinator strategies have been adopted in several countries, including the UK, the USA, Brazil and Ireland, along with the global Coalition of the Willing on Pollinators.
- The Kunming–Montreal Global Biodiversity Framework (2022) includes targets on pesticide risk reduction and on restoring ecosystem services, including pollination.
- India has encouraged beekeeping and pollination-focused IPM through ICAR's All India Coordinated Research Project on Honey Bees and Pollinators.
Key points
- About 75% of leading crop types benefit from animal pollination, making up about 35% of production volume and worth US$235–577 billion a year (IPBES, 2016).
- Dependence ranges from none (rice, wheat, maize) to essential (melons, pumpkin, cocoa).
- Managed honey bee hive numbers have risen globally, but colony losses are high in some regions. Many wild bees and butterflies have declined, especially in Europe and North America.
- Drivers are habitat loss, pesticides (notably neonicotinoids), Varroa and pathogens, climate change and invasive species, acting together.
- Responses include safer pesticide use, flower-rich habitats, managed pollination, beekeeping support and policies such as the EU's neonicotinoid restrictions.
What the exams ask
- Explain the importance of pollinators for crop production and nutrition.
- List the drivers of pollinator decline.
- Describe neonicotinoids and the EU restrictions.
- Name pollinator-dependent crops and the recommended number of bee colonies per hectare.
- Suggest bee-friendly farm practices.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
Are honey bees endangered?
The western honey bee as a managed species is not endangered; hive numbers are rising worldwide. But beekeepers in some regions face heavy colony losses and costs. Many wild bee species, which often pollinate crops more efficiently per visit, are in real decline.
Do neonicotinoids alone explain bee decline?
No. They are one important stressor, especially where used widely as seed treatments, but habitat loss, poor nutrition, Varroa and viruses, and climate change all contribute. Most scientists see bee decline as the result of multiple interacting stresses.
Can hand pollination or drones replace bees?
Only on a small scale. Hand pollination is used in some apple and pear orchards in China and in vanilla, but it is labour-intensive. Robotic and drone pollination remain experimental. Wild and managed pollinators provide the service far more cheaply.
Sources
- IPBES. The Assessment Report on Pollinators, Pollination and Food Production. IPBES Secretariat, Bonn, 2016.
- Klein, A.-M. et al. "Importance of pollinators in changing landscapes for world crops." Proceedings of the Royal Society B 274, 303–313 (2007).
- Potts, S. G. et al. "Safeguarding pollinators and their values to human well-being." Nature 540, 220–229 (2016).
- Goulson, D., Nicholls, E., Botías, C. and Rotheray, E. L. "Bee declines driven by combined stress from parasites, pesticides, and lack of flowers." Science 347, 1255957 (2015).
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