Pollinator Limitation Is Reducing Global Food Crop Yields

Many of the food crops we most enjoy worldwide are falling short of their potential because pollinating insects are visiting them less often, according to a new study.

Insects that perform the vital task of pollination are declining on a large scale, with major implications for food production: 75 percent of the world's crops rely at least partly, and sometimes wholly, on insect pollination.

Although staple crops such as rice and wheat are not included in that figure, pollination remains vital for what the study's lead author, Rutgers University ecologist Katherine Turo in the US, calls "nutrient-dense and interesting foods that we like and are culturally relevant".

"If you look through a list of crops and think about which fruits and vegetables you're most excited to eat – like summer berries or apples and pumpkins in the fall – those are the crops that typically need to be pollinated by insects," Turo says.

Pollinator limitation in global food crops

Experimental research into pollinator limitation in crops remains limited. Scientists already know that it affects worldwide food supplies, but the scale of its occurrence has not previously been clear.

A large number of studies have calculated maximum possible yields using hand pollination, an approach that may exaggerate pollen limitation. Measuring real-world effects directly - by recording insect visits to crop flowers alongside the yields that follow - offers a more realistic assessment.

To establish the extent to which pollinator limitation is reducing food production, the multinational research team examined one of the most extensive global datasets on crop pollination. It covers 32 leading commercial crops and commodities that depend on pollinators.

The open-source CropPol database is an international project that has, so far, compiled three decades of information on crop pollinators, flower visits and pollination.

Using this detailed resource, Turo and her colleagues determined that inadequate pollination limits as many as 60 percent of crop systems worldwide. Of the 49 crop species assessed, 25 were affected, with blueberry, coffee and apple crops experiencing the greatest impact.

Pollinator limitation was present in 85 percent of the countries included in the database, across all six represented continents.

"Our findings are a cause for concern and optimism," says Turo.

"We did detect widespread yield deficits. However, we also estimate that, through continued investment in pollinator management and research, it is likely that we can improve the efficiency of our existing crop fields to meet the nutritional needs of our global population."

Improving crop yields through pollinator visits

The researchers calculated that lifting pollinator visits in fields with low visitation to the levels recorded in the highest-performing fields could reduce the difference between low- and high-yielding fields by 63 percent.

"If field managers could improve consistency across high- and low-yield fields, much of the observed yield problems could be addressed," Turo says.

The team also found that pollinator limitation was marginally less probable where more forest covered land within 1 kilometre (0.6 miles) of a field. While the pattern was not universal, it suggests that the broader ecosystems around farmland could contribute to the survival of beneficial insects.

However, the authors found no shared patterns among the 12 datasets most strongly influenced by forests. They therefore say more research is necessary to understand how sensitive pollinators are to forested land cover.

"Crop yields, which measure the amount of crops grown per unit area of land, are relevant to assessing the adequacy of the world's food supply relative to its population," Rutgers ecologist Rachael Winfree says.

"Our findings show that by paying more attention to pollinators, growers could make agricultural fields more productive."

Threats to insect pollinators

Achieving this may be more difficult than it appears. Insects face a lethal combination of disease, pesticides, changing seasons and habitat loss.

Putting a value on the services provided by these small yet powerful allies to billion-dollar industries may encourage us to treat the dangers confronting them more seriously.

The research is published in Nature Ecology & Evolution.