Crop Pests Move Polewards to Flee Warming Climate, Threaten Global Food Security
By Tim Radford
A fungus is heading your way. The caterpillars are on the march. So are viruses and any number of insects and nematode worms, and since 1960 they have been shifting north and south at an average speed of three kilometers a year as the world warms, according to researchers at Exeter University in the UK.
Sandra Gurr and colleagues reported in Nature Climate Change that they looked at more than 26,000 observations of 612 well-known crop pests and had access to observations made much earlier, including the first record of fungus attack on oilseed rape in the UK in 1822.
Crop pests can cause famine, devastation and economic ruin. The nineteenth century Irish potato famine was caused by the pathogen Phytophthora infestans and the Great Bengal Famine of 1943 was blamed on the fungus Helminthosporium oryzae. And French winegrowers have never forgotten or forgiven the Phylloxera aphid that destroyed the vineyards.
But losses to crop pests are a quiet disaster now: they routinely destroy between 10 percent and 16 percent of all crops—a lost harvest that would otherwise feed more than eight percent of the planet’s people.
And, warned Gurr and her co-authors, crop pests are still a threat to food security. The spread of pests towards the poles is certainly helped by human activity and they believe the most effective agency is international freight transport.
But global warming is making it a little easier every year for the pests to find a comfortable home and easy pickings in previously unsuitable regions.
The mountain pine beetle Dendroctonus ponderosae has destroyed large areas of pine forest in the U.S. Pacific Northwest. Rice blast fungus has now reached 80 countries, has had a dramatic effect on agricultural economies and on local ecosystems, and—ominously—has evolved to develop a taste for wheat. Wheat blast is now a big problem in Brazil.
One reason for concern is that countries at higher latitudes—essentially, the developed world—are better able to monitor and manage emerging pests and diseases. But these are also the countries with the highest yields per hectare.
If climate change makes it easier for crop diseases to spread, then there must be even more effort to watch out for new infestations and to control the spread of diseases. There is simply more to lose.
“Renewed efforts are required to monitor the spread of crop pests and to control their movement from region to region if we are to halt the relentless destruction of crops across the world in the face of climate change,” said Professor Gurr.
“If crop pests continue to march polewards as the Earth warms the combined effects of a growing world population and the increased loss of crops to pests will pose a serious threat to global food security,” said Gurr's colleague Dan Bebber.
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