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Battling the bread bugs

Sunn Pest feeding on wheat spikes
Sunn Pest feeding on wheat spikes
credit: ICARDA

Wheat is central to the diets of people in the West and Central Asia and North Africa region, but it is in short supply in many countries of the region because it is vulnerable to insect attack. Sunn pest, an insect pest from the shield bug and stink bug families, reduces wheat and barley yields significantly and renders flour unsuitable for bread-making. The traditional approach to control has been government-funded aerial spraying, which drains more than $150 million each year from the already stretched agricultural budgets. However, in recent years, pest resistance appears to be increasing and the effectiveness of pesticide-based control has been questioned. Supported by a consortium of international and regional scientists, policy changes are being effected as integrated pest management (IPM) methods gain recognition within the region.

Wheat provides up to 40 per cent of daily calories and protein among the region's population but the problem of Sunn pest has resulted in severely reduced yields - often three times lower than the world's average of 5 tonnes per hectare. More than 15 million hectares of wheat and barley cultivation are now affected by this pest. As well as feeding on plants, the insects also inject an enzyme into the grain which destroys its natural gluten. As a result, grain with even a low level of infestation (less than five percent) is unsuitable for making bread, and sells for much less than the normal market price.

Challenging pesticide policy

Changing government attitudes towards aerial spraying has been a key achievement of the consortium, which brings together scientists from several international institutions* and the national agricultural research systems of Iran, Syria and Turkey. Sunn pest control in the region has traditionally been a government responsibility; when outbreaks occur, farmers inform local authorities, who request the government to carry out spraying. But the dependence on pesticides has many drawbacks, besides chemical costs and concerns over the development of resistance; water courses are frequently polluted and native beneficial parasite and predator insect populations are destroyed.

Regional research by the consortium has demonstrated that aerial-spraying is counter-productive, and far less effective than alternative methods provided by IPM. With policy-makers and other government representatives involved with the consortium from its early stages, important changes in policy have been achieved. In Turkey and Iran for example, over three million hectares are now under a system of farmer-based control, resulting in significant savings and reduction of Sunn pest damage.

Persuading farming organisations and individual farmers to take control of Sunn pest management has been vital for implementing effective IPM strategies. Through field schools, farmers have learned improved scouting techniques and adopted higher economic thresholds for pesticide application, reducing the frequency of chemical use. This has been one part of a wider approach to boost beneficial insect populations. Farmers have also been encouraged to leave shelter belts of uncultivated land around wheat fields, to provide a habitat for Sunn pest natural enemies. Other methods include the use of cardboard incubators containing hundreds of Sunn pest eggs, each of which has been deliberately infected by a parasite, a hymenoptera wasp. These are placed in wheat fields, where the wasps hatch and subsequently parasitise more Sunn pest eggs.

Hitting pests at rest

A farmer in Turkey about to release a Sunn pest predator, the partridge
A farmer in Turkey releases a partridge - a predator of Sunn Pest
credit: ICARDA

Sunn pest insects spend much of the year in over-wintering grounds, buried in leaf litter at the foot of pine or oak trees, or in the grass along river banks. During this time they are vulnerable to attack by birds, and in Turkey, partridges have been mass reared and released into the over-wintering grounds to reduce pest numbers.

Meanwhile, international partners have been spearheading work to develop a fungus-based biopesticide. Indigenous fungal strains have been collected and characterised to determine their pathogenic potential, and mass production techniques have been devised to make simple, region-specific formulations. In field trials, several have shown the potential to persist for more than a year, reducing the need for reapplication, and have achieved mortality rates of over 90 per cent. The fungal products could be marketed in the future as granular and oil-based formulations, and will be ideal for clearing infestation in over-wintering sites. A spray for killing juvenile insects in the field is also being tested.

The development of agreed protocols for assessing infestation has allowed scientists from across the region to compare control strategies. As a result, policies adopted in one country have, in several instances, been taken up by others. Through training workshops, conferences and local language publications, the research has gained recognition across the region, influencing control strategies in Uzbekistan, Kyrgyzstan and Kazakhstan, Iraq and Afghanistan.

The International Centre for Agricultural Research in the Dry Areas (ICARDA) has established a biopesticides facility to conduct further research on fungal-based management and provide a training site for regional capacity-building. The Centre is also conducting field-based screening of wheat cultivars for Sunn pest resistance. Several cultivars have been selected, and are now being used for varietal development by wheat breeders. Finding ways of boosting grain production and reducing pest damage in Central and West Asia and North Africa is of high priority, following a recent prediction that grain shortage in the region will reach 80 million tons per year by 2025.

*including the International Centre for Agricultural Research in the Dry Areas (ICARDA), the University of Vermont Entomology Research Laboratory (UVM) and CABI Bioscience

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1st November 2006