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Plants under attack send finely-tuned aromatic cry for help

11 February 2010

Researchers from Rothamsted Research, an institute of BBSRC, have found that plants under attack by insect herbivores emit repellent smells to deter insect feeding. These odours often act as distress signals, which attract natural enemies of the insect pests. The research, carried out in collaboration with the International Centre for Insect Physiology and Ecology (icipe) in Kenya, reveals that the quality of these signals in terms of blend composition and chemical identity can be more important than the total amount of odour released. This study is published in the Royal Society journal Biology Letters.

The researchers observed changes in odour profiles emitted from signal grass, an important livestock forage crop in Africa, when under attack by spotted stemborer moths. Typically, insect attack leads to an increase in odour emission but here an unusual phenomenon was found where suppression of the main odour emitted occurred when the moths laid eggs. This changed the ratio of compounds in the odour blend but nevertheless led to insect behavioural responses that are beneficial to the plants. The odour of plants with eggs was more attractive to parasitic wasps, the natural enemies of stemborers.

Dr Toby Bruce said “These wasps are important natural enemies of the stemborer pest studied. They have evolved chemosensory systems that are fine-tuned for recognition of plant odours that signal the presence of their prey.” “Even though overall odour emission was reduced the wasps were more attracted to the odour of plants with eggs that the odour of plants without eggs. This showed that it is Quality not Quantity that is important in these interactions”.

There is an urgent need in most of rural Africa, where farmers cannot afford chemical pesticides, for crop varieties that can naturally defend themselves against insect pests. The odour-based communication between plants and natural enemies of insects that has been revealed in this study could provide insights into selecting and breeding crop varieties with better potential for induced early defence against pests such as stemborers.


Notes for editors

  1. The research will be published in the June issue of Biology Letters (Published online before print 23 December 2009, doi: 10.1098/rsbl.2009.0953, and available online at as “Is quality more important that quantity? Insect behavioural responses to changes in a volatile blend after stemborer oviposition on an Africa grass” by Toby J. A. Bruce, Charles A. O. Midega, Michael A. Birkett, John A. Pickett and Zeyaur R. Khan. The study was funded by the UK Biotechnology and Biological Sciences Research Council (BBSRC). The research at ICIPE is funded by the Gatsby Charitable Foundation and Kilimo Trust (2006-2009).

    For further information, please contact Dr. Toby Bruce: Tel: +44 (0)1582 763133 ext 2682,

  2. Rothamsted Research is centred in Harpenden Hertfordshire and is the largest agricultural research institute in the country. The mission of Rothamsted Research is to be recognised internationally as a primary source of first-class scientific research and new knowledge that addresses stakeholder requirements for innovative policies, products and practices to enhance the economic, environmental and societal value of agricultural land. The Applied Crop Science department is based at Broom's Barn, Higham, Bury St. Edmunds. North Wyke Research is located near Okehampton in Devon. See
    For further information, please contact the Rothamsted Research Press Office Tel: 01582 763133 ext 2757 or email Dr Sharon Hall (

  3. BBSRC is the UK funding agency for research in the life sciences. Sponsored by Government, BBSRC annually invests around £450 million in a wide range of research that makes a significant contribution to the quality of life in the UK  and beyond and supports a number of important industrial stakeholders, including the agriculture, food, chemical, healthcare and pharmaceutical sectors.

    BBSRC provides institute strategic research grants to the following:
    The Babraham Institute, Institute for Animal Health, Institute for Biological, Environmental and Rural Studies (Aberystwyth University), Institute of Food Research, John Innes Centre, The Genome Analysis Centre, The Roslin Institute (University of Edinburgh) and Rothamsted Research. The Institutes conduct long-term, mission-oriented research using specialist facilities. They have strong interactions with industry, Government departments and other end-users of their research.

    For more information see:

  4. icipe is a tropical organisation established in Kenya in 1970 to research tropical insects and their impact on food security and health. icipe's mission is to help alleviate poverty, ensure food security and improve the overall health status of peoples of the tropics by developing and extending management tools and strategies for harmful and useful arthropods, while preserving the natural resource base through research and capacity building. See

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