Pest warning

Crop pests are adapting to climate change and are evolving to spread to new areas to wreak more havoc. Dan Bebber from the department of biosciences at the University of Exeter, UK, reviewed the literature on impact of climate change on crop pests. He illustrates his findings through example of the Colorado potato beetle, which is originally from southwestern US, entered France in the 1950s and invaded most European and central Asian countries. By the 1990s, it reached China from Kazakhstan and moved towards Russia. It is difficult to predict the beetle’s migratory course as prediction models do not take into account the insect’s evolution and highly adaptable nature.

“Our review has highlighted how difficult it is to predict where damaging crop pests may turn up. Their ability to evolve tolerance to different climates has been investigated in only a few species but has not been considered in distribution models. We urgently need to improve monitoring and identification of these pests, particularly in the developing world, both for research as well as to secure food production,” says Bebber (see ‘Climate change is...’). The review was published in the Annual Review of Phytopathology on August 4, 2015.

Pest evolution

There have been many studies to investigate the movement, changes, and impacts of a variety of agricultural killers—viruses, fungi, insects and weeds. For instance, scientists have found out that potato leafhoppers, migratory pests in the US, have been arriving 10 days earlier than normal on an average over the last 62 years, and their infestations are severe. Entomologists at the University of Maryland and Queens College at the City University of New York analysed data from 1951 to 2012 and predicted that continued global warming could advance the time of insect’s colonisation and also increase their impact on the affected crops. “Climate change is not just costly because temperatures and oceans rise, but because it makes it harder to feed ourselves,” says Mitchell Baker, one of the authors of the research, which was published in PLOS ONE on May 13, 2015. “Increased pest pressure in agriculture is one of the complex effects of continued warming. Predicting arrival time and severity is critical to manage these pests,” adds Baker.

In an earlier study, Bebber, in association with the University of Oxford found that global warming had led to the spread of crop pests towards the North and South Poles at a rate of three km per year. The study demonstrates a strong connection between increased global temperatures and the range of expansion of crop pests. The researchers analysed observations of the distribution of 612 crop pests obtained over the last five decades. The study states that global warming has resulted in the spread of crop pests to regions which were previously considered unsuitable for habitation. “If crop pests continue to march pole wards as the earth warms, the combined effects of a growing world population and the increased loss of crops due to pests, will pose a serious threat to global food security,” says Bebber.

Invading India

The western flower thrips (Frankliniella occidentalis), an invasive pest native to the US, and another pest, tomato leafminer (Tuta absoluta) from south America entered India in 2013 and 2014 respectively. Scientists are considering climate change as one of the reasons for their entry, along with human traffic and trade. Already, the spot blotch disease is affecting the wheat plant and the severe occurrence of Indian cassava mosaic virus in Kerala is due to a shift in climatic conditions. Chirantan Chattopadhay, director, ICAR-National Research Centre for Integrated Pest Management (NCIPM), New Delhi, says the incidence of the Africa cassava mosaic virus and the Sri Lankan cassava mosaic virus in India is due to an increase in temperatures and carbon dioxide levels.

These changes are significant as India loses about 15-25 per cent of crops yields each year due to pest attacks, which amounts to Rs 0.9-1.4 lakh crore annually, says Chattopadhay. Significantly, the allocation by the Union government for agriculture has been declining—from Rs 19,852 crore in 2014-15 to Rs 17,004 crore in 2015-16.

The frequency of new pest introductions will increase and also the occurrence of major pest outbreaks will increase, says the Climate Change, Agriculture and Food Security (CCAFS), a research programme by the Consortium of International Agricultural Research Centers (CGAIR), in its 2015 report on Africa. “These events will be driven by outcomes associated with climate change and extreme weather,” says the report. With climate change becoming one of the core drivers for the migration of new pests to newer areas, integrated pest management strategies must factor these virulent guests. Unfortunately, the Union government seems to have little money and even lesser foresight to ensure food security.

'Climate change is creating new spaces for pests'   Dan Bebber of the University of Exeter, the UK, has published a review on the impact of climate change on crop pests. He talks about the reasons pests are spreading globally and inadequacies in our prediction models Is the distribution of crop pests and pathogens across the world a serious concern? Highly virulent strains are evolving rapidly and these organisms are destroying huge amounts of food. For example, the new Lethal Necrosis disease, which evolved in Africa, kills maize plants and there is no cure for it. What's driving the distribution of the pests? The main driver is human activity such as trade of agricultural products and transport of live plants. Some organisms move by themselves, such as the wind-borne spores of fungi. Climate change is also making new areas suitable for certain pests and pathogens. What's wrong with the current system of prediction of pest movement? The most common methods look only at the suitability of the climate. They do not take into account the availability of host plants, trade routes, and the evolution of pests and pathogens. How can we control the problem? We need better monitoring and reporting of where pests and pathogens are located, particularly in the developing world.

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