Climate change, driven by human activity, is increasing the spread of crop pests both north and southwards at an average rate of almost 3km a year.

Researchers from the Universities of Oxford and Exeter have shown that increased global temperatures over the past fifty years have expanded the ranges of a number of crop pests. Having examined the distribution of over 600 crop pests since 1960, the scientists noted a " movement of pests north and south towards the poles, and into new previously un-colonised regions, [which] corresponds to increased temperatures."  

They found that, whilst some insect species had rapidly expanded their range (moving up to 12 miles each year), many species of bacteria had barely moved over the fifty year period.

Currently 10-16 percent of crop production is lost to pests worldwide. The researchers, whose paper was published on Sunday (1st September) in the journal Nature Climate Change, said that while some pests are expanding into areas that were once too cold for them, the pests' diversity is also increasing; new strains are continually evolving.

They estimated that crop losses to fungi alone could otherwise feed nine percent of the current global population. Worryingly, they said that the identified trend in the spread of pests is set to continue if global temperatures continue to rise as predicted.

The spread of pests is believed to be caused by a combination of natural processes and human activity. International freight transportation plays the most significant role, according to the scientists, but conditions in new regions must be suitable for the pests to take hold.

Illustrating their findings, the team from Oxford and Exeter used the example of rice blast, a devastating fungus, present in over 80 countries, which has now moved to wheat. Considered to be a new disease, wheat blast is sharply reducing wheat yields in Brazil and, though its spread has so far been limited to South America, research is already underway to prevent the fungus from moving further North. 

Dr Dan Bebber from the University of Exeter said, "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."

Dr Bebber said that efforts must be made to increase biosecurity in a bid to combat the spread of plant diseases and protect agricultural systems. One of the most worrying results of the spread is that crop pests appear to be entering new areas faster than their predators, meaning they are free to do more damage; earlier studies have suggested that wildlife and plants are shifting their distribution at a slower rate and that this is often hindered by human activity, which appears to be helping the spread of pests.

Commenting on the study's implications, professor Sarah Gurr, also of the University of Exeter, added, "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."