Evidence for and causes of pollinator declines

Globally, pollinators are in decline
World-wide, pollinator populations are shrinking. Several overlapping factors contribute to this disturbing global trend, including habitat fragmentation, pesticide use, climate change, and the spread of emergent pathogens, parasites and predators. In the US, beekeepers have lost ~30% of their colonies every year since 2006, with total annual losses sometimes reaching as high as 42% (Bee Informed Partnership). Monarch populations are also at risk, due to the habitat degradation of southern overwintering sites and the limited availability of milkweed plants along their U.S. migration routes. Population changes in other insect pollinator species, including wild bee species, flies, butterflies and beetles have also been observed, although limited historical data is available to quantify these declines. Indeed, there are several hundred thousand species of pollinators and tracking all of them is not possible. However, surveys have documented disturbing population declines and even local extinctions of select pollinator species across Europe and the US.

What is causing these declines?
Wild and managed pollinators face numerous stressors. Honey bees, other managed pollinator species such as bumble bees and orchard bees, and wild bees suffer from exposure to parasites and pesticides, and loss of floral abundance and diversity due to increased land-use. In addition, habitat destruction limits nesting sites for wild pollinators, including important butterfly and moth species. Unfortunately, these stressors may interact synergistically to produce more detrimental effects on pollinator health.

Beekeeper Chemicals

Minimizing exposure: using Integrated Pest Management (IPM) to reduce beekeeper-applied chemicals by Holly Holt, PhD

Habitat Fragmentation

No-bees’ land: habitat loss and fragmentation leave pollinators stranded by Holly Holt, PhD


Neonicotinoids: a dangerous harvest by Holly Holt, PhD

Nesting Sites

Hollow sticks, cracked stones and other places bees call home: nesting habitat for bees by Holly Holt, PhD


Intestinally indisposed: Nosema infection in honey bees by Holly Holt, PhD


Poor nutrition spells poor prospects for pollinators by Holly Holt, PhD

Parasatoids and Cleptos

Body snatchers and pollen thieves: bee nurseries are other insects’ cafeterias by Holly Holt, PhD


Viruses, bacteria and fungi are microbial pathogens that bug bees by Holly Holt, PhD


Pesticides and pollinators: the good, the bad and the unknown by Holly Holt, PhD

Small Hive Beetles

Mobbed: small hive beetles are an invasive threat to bees by Holly Holt, PhD

Global Warming

Global warming threatens pollinators and people by Holly Holt, PhD