Image caption The team looked at more than 600 pests, including the Colorado potato beetle

Climate change is helping pests and diseases that attack crops to spread around the world, a study suggests.

Researchers from the universities of Exeter and Oxford have found crop pests are moving at an average of two miles (3km) a year.

The team said they were heading towards the north and south poles, and were establishing in areas that were once too cold for them to live in.

The research is published in the journal Nature Climate Change.

Currently, it is estimated that between 10% and 16% of the world's crops are lost to disease outbreaks. The researchers warn that rising global temperatures could make the problem worse.

Dr Dan Bebber, the lead author of the study from the University of Exeter, said: "Global food security is one of the major challenges we are going to face over the next few decades.

"We really don't want to be losing any more of our crops than is absolutely necessary to pests and pathogens."

Trade transport

To investigate the problem, the researchers looked at the records of 612 crop pests and pathogens from around the world that had been collected over the past 50 years.

The most convincing hypothesis is that global warming has caused this shift Dr Dan Bebber, University of Exeter

These included fungi, such as wheat rust, which is devastating harvests in Africa, the Middle East and Asia; insects like the mountain pine beetle that is destroying trees in the US; as well as bacteria, viruses and microscopic nematode worms.

Each organism's distribution was different - some butterflies and insects were shifting quickly, at about 12 miles (20km) a year; other bacterium species had hardly moved. On average, however, the pests had been spreading by two miles each year since 1960.

"We detect a shift in their distribution away form the equator and towards the poles," explained Dr Bebber,

The researchers believe that the global trade in crops is mainly responsible for the movement of pests and pathogens from country to country.

However, the organisms can only take hold in new areas if the conditions are suitable, and the researchers believe that warming temperatures have enabled the creature to survive at higher latitudes.

Dr Bebber said: "The most convincing hypothesis is that global warming has caused this shift.

"One example is the Colorado potato beetle. Warming appears to have allowed it to move northwards through Europe to into Finland and Norway where the cold winters would normally knock the beetle back."

The researchers said that better information about where the pests and pathogens were and where they were moving was needed to fully assess the scale of the problem.

"We also need to protect our borders, we have to quarantine plants to reduce the chances that pests and pathogens are able to get into our agricultural systems," added Dr Bebber.