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Many of the world's most important crop-producing countries will be fully saturated with pests by the middle of the century if current trends continue, a study has found.

More than one-in-ten pest types can already be found in around half the countries that grow their host crops. 

And if this spread advances at its current rate, scientists fear that a significant proportion of global crop-producing countries will be overwhelmed by pests within the next 30 years.

Research from the University of Exeter says a warming Earth is influencing the distribution of crop pests. The scientists claim that many crop-producing countries could be saturated by pests by 2050, posing  'a grave threat to global food security'. Pictured is the root knot nematode (Meloidogyne incognita) on a tomato plant

The research from the University of Exeter was published in the journal Global Ecology and Biogeography.

It describes the patterns and trends in the spread of crop pests, using global databases to investigate the factors that influence the number of countries reached by pests and the number of pests in each country.

Crop pests include fungi, bacteria, viruses, insects, nematodes, viroids and oomycetes.

'If crop pests continue to spread at current rates, many of the world's biggest crop producing nations will be inundated by the middle of the century, posing a grave threat to global food security,' said Dr Dan Bebber of the Biosciences department at the University of Exeter.

The study identifies the pests likely to be the most invasive in coming years, which includes three species of tropical root knot nematode whose larvae infect the roots of thousands of different plant species.

Another, Blumeria graminis, is a fungus that causes powdery mildew on wheat and other cereals.

And the Citrus tristeza virus (given its name meaning 'sadness' in Portuguese and Spanish by farmers in the 1930s) is also a threat, having reached 105 of 145 countries growing citrus by the year 2000.

Fungi lead the worldwide invasion of crops and are the most widely dispersed group, despite having the narrowest range of hosts.

Crop pests include fungi, bacteria, viruses, insects, nematodes, viroids and oomycetes. This map shows the global distribution of the Citrus tristeza virus, compiled by the Plantwise Knowledge Bank based on published reports in scientific literature, which reached 105 of 145 countries growing citrus by the year 2000

The study looked at the current distributions of 1,901 crop pests and pathogens and historical observations of a further 424 species. 

Significant use was made of historical CABI (Centre for Agriculture and Biosciences International) records, which document crop pests and diseases around the world from 1822 to the present day.

'By unlocking the potential to understand the distribution of crop pests and diseases, we're moving one step closer to protecting our ability to feed a growing global population,' said Dr Timothy Holmes, Head of Technical Solutions at CABI's Plantwise Knowledge Bank.

'The hope is to turn data into positive action.'

It supports the view of previous studies that climate change is likely to significantly affect pest pressure on agriculture, with the warming Earth having a clear influence on the distribution of crop pests.

The authors also describe the global game of cat-and-mouse as crops are introduced to pest free regions and briefly thrive, before their pursuers catch up with them.

Professor Sarah Gurr of Biosciences the University of Exeter added: 'New, virulent variants of pests are constantly evolving. 

'Their emergence is favoured by increased pest population sizes and their rapid life-cycles, which force diversified selection and heralds the appearance of new aggressive genotypes. 

'There is hope if robust plant protection strategies and biosecurity measures are implemented, particularly in the developing world where knowledge is scant. 

'Whether such precautions can slow or stop this process remains to be seen.'