Crops are increasingly being eaten by insects because of climate change

Crops are increasingly being eaten by insects because of manmade climate change, according to new research.

The phenomenon is occurring despite declining populations of caterpillars, beetles, grasshoppers and other critters.

Plants are around a quarter more likely to be damaged than specimens collected just over a century ago.

Burning of fossil fuels, urbanisation and the introduction of invasive species are being blamed.

The shock finding is based on an analysis of leaves dating back 67 million years – just before the asteroid impact that wiped out the dinosaurs.

It has implications for feeding the world. The global population will reach nearly 10 billion by 2050.

Lead author Dr Lauren Azevedo-Schmidt said: ‘Our results demonstrate plants in the modern era are experiencing unprecedented levels of insect damage – despite widespread insect declines.’

The disparity can be explained by human activities, say the University of Wyoming team. They examined leaves with different signs of feeding from the Late Cretaceous through the Pleistocene era – a little over two million years ago.

There were marked increases in others collected from three modern forests compared to the fossil record.

The first study of its kind adds to evidence each degree of global warming will increase loss of fruits, vegetables and cereals by up to 25 per cent.

Insect appetites surge when the thermometer rises. Prolonged droughts or floods will exacerbate the problem.

Dr Azevedo-Schmidt, now at Maine University in New England, said: ‘Our work bridges the gap between those who use fossils to study plant-insect interactions over deep time and those who study such interactions in a modern context with fresh leaf material.

‘The difference in insect damage between the modern era and the fossilised record is striking.’

More research is necessary to determine the precise causes. But a warming climate, urbanisation and invasive species are likely to have had a major impact.

Dr Azevedo-Schmidt said: ‘We hypothesise humans have influenced insect damage frequencies and diversities within modern forests – with the most human impact occurring after the industrial revolution.

‘Consistent with this hypothesis, herbarium specimens from the early 2000s were 23 per cent more likely to have insect damage than specimens collected in the early 1900s – a pattern that has been linked to climate warming.’

Insects and the plants they feed on have been engaged in a co-evolutionary battle for millions of years to eat or not be eaten.

Dr Azevedo-Schmidt said: ‘This research suggests the strength of human influence on plant-insect interactions is not controlled by climate change alone but, rather, the way in which humans interact with the terrestrial landscape.’

Experts fear warmer temperatures could tip the balance in favour of insects and spell danger for crops and the farmers that tend to them.

Unlike animals, plants cannot run or hide from predators. Instead, they produce an arsenal of toxic chemicals that repel attack by insects and other plant consumers.

Producing these compounds is costly and often stunts their growth. So plants deploy this chemical defence arsenal only when damaged by a chewing insect.

It’s estimated agricultural productivity must double in the next 30 years to meet demands.

Current yield trajectories for major crops, combined with the uncertain impacts of a changing global environment, suggest the world will fall well short of this demand using conventional agricultural practices.

The Royal Society and other scientific organisations have called for a Second Green Revolution that will permit the sustainable intensification of agriculture through development of crops that are more resilient in face of increasingly harsh environmental conditions.

Recent technological advances, from genomics and gene editing to computational and data science approaches, provide researchers with unprecedented opportunities to work toward this goal.

The study is in Proceedings of the National Academy of Sciences.

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