Pollinator decline: what is actually happening

Three separate things called one thing

The drivers, as identified

IPBES identifies several interacting drivers rather than a single cause, and the interaction is part of the finding — a colony coping with poor forage handles a pathogen load worse than a well-fed one.

• Habitat loss and land-use change. The largest driver. Britain lost around 97% of its species-rich grassland during the twentieth century, and that is the flora most specialist bees depended on.
• Agricultural intensification. Large monocultures produce a feast-then-famine forage landscape, remove field margins and hedgerows, and eliminate the bare undisturbed ground many solitary bees need to nest in.
• Pesticides. Insecticides kill directly; sublethal doses impair navigation, foraging and reproduction. Herbicides act indirectly by removing the flowers. Effects are documented most thoroughly for honey bees and least for the solitary species most likely to be affected.
• Pathogens and parasites. Varroa destructor and its viruses for honey bees; pathogen spillover from managed colonies — including commercially reared bumblebees — into wild populations.
• Invasive species, including introduced bees competing with natives and invasive predators such as the yellow-legged hornet.
• Climate change. Range shifts, and mismatches where a bee's emergence and its host plant's flowering move by different amounts. Montane and northern bumblebees are being squeezed from the warm end without gaining ground at the cold end.

What the evidence does not settle

None of this undermines the finding that wild pollinators are declining where we can measure. It does mean that confident global percentages should be treated with suspicion, and that the honest version of the story includes what is not known.