By Roberta Attanasio
One of the major global threats to food security is the current spread of crop pests, unintentionally moved by human activity across world regions at unprecedented rates.
Crop pests include viroids, viruses, bacteria, oomycetes, fungi, nematodes, and insects. In the past, this spread was limited by physical barriers such as mountains, seas and deserts. However, such natural limits are now bypassed because of the rapid increase in international and intercontinental agricultural trade.
To date, more than 12,000 alien species have been documented in Europe by DAISIE (Delivering Alien Invasive Species Inventory for Europe), a unique three-year research project involving more than 100 European scientists and funded by the European Union. Many of these species are insects.
Indeed, it seems Europe has already been invaded by over 1,000 insects, including some of the most invasive species, such as the Tobacco Whitefly (Bemisia tabaci), the Western Corn Rootworm (Diabrotica virgifera) and the Colorado Potato Beetle (Leptinotarsa decemlineata).
What are invasive alien species? According to the International Union for Conservation of Nature, invasive alien species are animals, plants or other organisms introduced by man into places out of their natural range of distribution, where they become established and disperse, generating a negative impact on the local ecosystem and species.
Several factors contribute to the spread of invasive alien species. Border controls form the last line of defense against these invasions – inspectors intercept and stop consignments that are contaminated with harmful alien species. Insufficient border controls may lead to increased spread. Results from a study entitled “Gaps in Border Controls Are Related to Quarantine Alien Insect Invasions in Europe” and published last year in the scientific journal PLOSone, suggest that European countries with gaps in border controls are subjected to invasion by higher numbers of insect pests.
Although spread of crop pests is facilitated primarily by human transportation, increasing concerns are related to the effects of climate change — climate change allows the establishment of pests in previously unsuitable regions.
Indeed, results from a new study entitled “Crop pests and pathogens move polewards in a warming world” (published yesterday in the scientific journal Nature Climate Change) indicate that global warming is resulting in the spread of crop pests and pathogens towards the North and South Poles at a rate of nearly 3 km a year.
The study is based on the analysis of published observations collected over the past 50 years. It examines the distribution of 612 crop pests and pathogens to conclude that their movement north and south towards the poles, and into previously un-colonized regions, corresponds to increased temperatures during that period.
Daniel Bebber, lead author of the study, 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.”
An example of pests that impact major world crops are the rice blast and wheat blast. Rice blast is a devastating disease caused by the fungal pathogen Magnaporthe oryzae. It results in lesions found on all parts of the plant, including leaves, leaf collars, necks, panicles, pedicels, and seeds and costs an estimated $66 billion in annual losses worldwide.
The Department of Plant Biology (The Ohio State University) reports that, in an alarming development, wheat blast, caused by a related fungus, Magnaporthe grisea, has emerged in South America and, recently, has been detected in Kentucky.
What are possible solutions to these problems? At the local level, crop diversification is one of them, as it slows down the spread of pathogens and pests. A survey published in the March 2011 issue of the scientific journal BioScience highlights multiple instances of farmers succeeding in protecting crops (such as rice and other cereals, alfalfa, and coffee) from outbreaks of pests and related disease often associated with climate change.
The farmers switched from growing a single variety of crop to growing a broader range of species or varieties, either at the same time or in rotation. An additional approach to crop diversification involved the introduction of structural variety into uniform fields. Fortunately, farmers have now increasing access to crop modeling techniques that can evaluate when a given adaptation technique might provide benefits.
However, climate change is an ongoing and extremely complex process. Old and new environmental problems related to the spread of crop pests can only be effectively tackled at the international level by developing new paradigms – paradigms that must overcome the challenges deriving from the different needs of countries and regions and from their different ability to develop and adopt new tools and strategies.