Common air pollutants from both urban and rural environments may be reducing
the pollinating abilities of insects by preventing them from sniffing out
the crops and wildflowers that depend on them, new research has shown.
Scientists from the University of Reading, the UK Center for Ecology &
Hydrology, and the University of Birmingham found that there were up to 70%
fewer pollinators, up to 90% fewer flower visits and an overall pollination
reduction of up to 31% in test plants when common ground-level air
pollutants, including diesel exhaust pollutants and ozone, were present.
The study, published in the journal Environmental Pollution, is the first to
observe a negative impact of common air pollutants on pollination in the
natural environment. The theory is that the pollutants react with and change
the scents of flowers, making them harder to find.
Dr. Robbie Girling, Associate Professor in Agroecology at the University of
Reading, who led the project, said: "We knew from our previous lab studies
that diesel exhaust can have negative effects on insect pollinators, but the
impacts we found in the field were much more dramatic than we had expected."
Dr. James Ryalls, a Leverhulme Trust Research Fellow at the University of
Reading, who conducted the study, said: "The findings are worrying because
these pollutants are commonly found in the air many of us breathe every day.
We know that these pollutants are bad for our health, and the significant
reductions we saw in pollinator numbers and activity shows that there are
also clear implications for the natural ecosystems we depend on."
Previous laboratory studies by members of the Reading team have shown that
diesel fumes can alter floral odors. This work suggested that pollution
could contribute to the ongoing declines in pollinating insects, by making
it harder for them to locate their food—pollen and nectar.
The impact this phenomenon has in nature, where insects provide pollination
of important food crops and native wildflowers is less well understood, so
this new study aimed to gather evidence to investigate how air pollution
affects different pollinating insect species, some of which rely on scent
more than others.
The study, funded by the Natural Environment Research Council, used a
purpose-built fumigation facility to regulate levels of nitrogen oxides
(NOx) – present in diesel exhaust fumes—and ozone in an open field
environment. They then observed the effects these pollutants had on the
pollination of black mustard plants by free-flying, locally-occurring
pollinating insects over the course of two summer field seasons.
They used pollution concentrations well below maximum average
levels—equating to 40-50% of the limits currently defined by US law as safe
for the environment
This pales in comparison with the far higher levels of pollution that occur
around the world due to breaches of regulations. For example, outside of
London, a 2019 analysis showed illegal levels of nitrogen dioxide were
recorded in local authorities in large areas of northern England, including
Cheshire and Gateshead, and south England, including Wiltshire, Chichester
and rural areas such as the New Forest.
Observations revealed there were 62-70% fewer pollinator visits to the
plants located in polluted air. This reduction was seen in seven pollinator
groups, particularly bees, moths, hoverflies and butterflies. There were
also 83-90% fewer flower visits by these insects, and ultimately a 14-31%
reduction in pollination, based on seed yield and other factors.
Such findings could have wide ranging implications because insect
pollination delivers hundreds of billions of pounds worth of economic value
every year. It supports around 8% of the total value of agricultural food
production worldwide, and 70% of all crop species, including apples,
strawberries and cocoa, rely on it.
This research is part of continuing studies into the effects of air
pollution on insect health and their interactions with the environment by
researchers at the University of Reading.
Dr. Christian Pfrang, Reader in Atmospheric Science at the University of
Birmingham and a co-author on the study, said: "This truly
cross-disciplinary work demonstrated very clearly how atmospheric pollutants
negatively impact on pollination with direct consequences for food
production as well as the resilience of our natural environment."
Reference:
James M.W. Ryalls et al, Anthropogenic air pollutants reduce insect-mediated
pollination services, Environmental Pollution (2022).
DOI: 10.1016/j.envpol.2022.118847