Plant Pest Interactions: How Soybean Aphids Trick Soybean Plant Defences

An Adult Soybean Aphid © Ho Jung Yoo, Purdue University (via Wikimedia Commons)

Following on from a previous blog on the interactions between soybean plants and soybean pests,  new research on soybean (Glycine max) responses to the soybean aphid (Aphis glycines) published in Molecular Plant-Microbe Interactions has revealed some of the complex and fascinating interactions between pests and their plant hosts.  This recent research led by Dr Gustavo Macintosh and Matthew Studham from Iowa State University has shown that soybean aphids can suppress the natural plant defense response of soybean plants to the aphids through the activation of what is known as an antagonistic decoy response. For example, the aphid will induce a plant defense that is not particularly effective against the pest (the ‘decoy’ defense) while suppressing the effective defense in order for it to continue feeding on the plant.  It has further been found that aphids can actively suppress the effective defence responses of the plant while at the same time ‘hijacking’ the plant metabolism to improve the nutritional value of the plant for their own benefit. Soybean aphids do this by inducing asparagine synthase transcripts which improve the nutritional content of the phloem sap from which they feed. Continue reading

The Soybean Gene: Scientists Discover the Key to Nematode Resistant Soybeans

Scanning electron micrograph of a soybean cyst nematode and egg © Ethan Hein via Flickr (License CC-BY-NC-SA 2.0)

Soybean (Glycine max) is an important crop that provides a sustainable source of protein and oil worldwide in countries such as the USA, Brazil, Argentina, India and many African countries, including Nigeria, South Africa and Uganda. The soybean cyst nematode Heterodera glycines is a microscopic roundworm that feeds on the roots of soybean and is a major constraint to soybean production. This nematode causes more than US$1 billion in yield losses annually in the United States alone, making it the most economically important pathogen on soybean. For over 50 years the planting of resistant cultivars and crop rotation have been the main management strategy for this pathogen, and only a few resistant plant types are used due to undesirable traits in other resistant varieties of soybean.  Moreover, the increase in virulent populations of the nematode on most known resistant plant sources coupled with the very limited knowledge of soybean resistance mechanism makes the development of new approaches for control of soybean cyst nematode a necessity. Continue reading

Plantwise plant clinics – Pest diagnosis for a farmer in Barbados

A farmer, Pedro Welch, attended the Plantwise plant clinic at this year’s Agrofest 2012, the annual agricultural show in Barbados. He described the problems he was having on his lime tree, and the plant doctor diagnosed the problem straight away, giving advice on how to manage the pest. Watch the video below to see a plant clinic in action.

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Coffee Berry Borer thriving due to Climate Change

A newly published paper has found that temperature increases are benefiting coffee berry borers in East Africa. The insects are causing more damage to coffee crops and it has also been reported that their distribution range has also expanded. The researchers behind the study also predict that the damage caused by the borers will worsen in the future.

Adult Coffee Berry Borer. Georg Goergen/IITA Insect Museum, Cotonou, Benin

The coffee industry is worth $90 billion dollars and involves around 25million coffee farmers across the tropics. It is an important crop for many farmers in developing countries and all efforts need to be taken to reduce pest damage.

The coffee berry borer, Hypothenemus hampei, is the most important pest of coffee worldwide. The Plantwise distribution map shows over 150 areas in which it has been reported. Continue reading

Pest-fighting Anthocyanins

U.S. Department of Agriculture (USDA) scientists in Illinois, USA, are investigating the role of anthocyanins in pest-control. They believe that the plant pigment can adversely affect crop pests such as the corn earworm caterpillar and the cabbage looper caterpillar that feed on it.

Cabbage looper caterpillar. Copyright A. Shelton.

Anthocyanins are a plant pigment which give blackcurrants and flowers, such as petunias, their blue and purple colour. They absorb blue-green and UV light, protecting plant cells from high-light stress.

In the experiments the scientists used corn earworm caterpillars (Helicoverpa zea). H.zea damage is usually serious and costly because of the larval feeding preference for the reproductive structures and growing points which are rich in nitrogen.

The caterpillars were forced to feed on blue areas of petunia petals which contained higher levels of anthocyanins than the white areas. It was found that these individuals gained less weight than other individuals which were fed on only the white leaf areas. Further experiments found that isolated anthocyanins slowed the caterpillar’s growth rate.

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Maize’s New Protector: Parasitic Wasps

Certain maize landraces obtained from South America have been found to have developed sophisticated defence strategies to cope with insect pests such as the spotted stemborer, Chilo partellus, it was reported today. These findings could help to increase maize yields and improve food security.

Parasitized spotted stemborer caterpillar. Note cocoon of the parasitic wasp Cotesia flavipes. © D. Cugala, Stemborer team, icipe

The spotted stemborer, Chilo partellus, is now a major pest in eastern and southern Africa, as well as South Asia where it causes yield losses of up to 88%. Since establishing in east Africa in the 1950s, it has spread to southern and central Africa. The distribution map on Plantwise.org shows the current distribution in Africa and South Asia.

The larvae tunnel extensively into stems and maize cobs causing weaknesses that may lead to stems breaking. They can also cause damage known as “dead heart”; this is when larvae crawl inside the sheath and tunnel into the heart of young shoots, killing the growing point, which leads to browning and wilting of the youngest leaves.

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Predicting the effects of global warming on insect pests

It has been estimated that presently pests cause 30-50% of yield losses to agricultural crops in developing countries and these rates are likely to increase with climate change. Although much attention has been given to the impacts of climate change on insect abundance and severity in temperate regions, little is known about potential impacts in tropical regions. Furthermore, recent studies suggest that climate change may favour pests over their natural predators, disrupting classical biocontrol of insect pests.

To address this gap, a new software, Insect Life Cycle Modelling (ILCYM),  was developed by The International Potato Center (CIP) to better estimate and to help mitigate the impacts of global warming on pest risk to food crops.

How is ILCYM used?

The “model builder” software supports the development of insect phenology models based on experimental temperature data of a specific insect, explained the model developers in a report, published in the CGIAR page. The module also provides tools to analyse an insect’s life-table and to validate existing models. The second module implements the CIP-developed temperature-driven phenology model in a GIS environment and allows for regional as well as global spatial simulation of insect activities (“pest risk mapping”). In its present version the software uses the phenology model of the potato tuber moth, Phthorimaea operculela, as an example, but can also be applied to other insect species.

The  effects of the 1997 El Niño event on Peru provided a preview of what global warming may bring.  Temperatures on the Peruvian coast were about 5°C higher than average and insect pest populations flourished, which prompted farmers to respond by applying high doses of pesticides every 2-3 days.

The ILCYM software is a new tool, which, it is hoped, will facilitate the development of insect phenology models and mapping of risk scenarios, highlighting places where training and adaptation efforts can be most effective.

CIP is coordinating further development of ILCYM and  its application to a wider range of insects in a new project. Collaborators include the International Centre of Insect Physiology and Ecology, the International Institute of Tropical Agriculture (IITA), the University of Hohenheim, Germany, under the CGIAR System-wide Program on Integrated Pest management, and partners at national agricultural research institutes and universities in Africa.

Link to CIP webpage.

Link to CGIAR System-wide Program on Integrated Pest Management (SP-IPM) report page.

Link to CGIAR’s climate change page.

Link to datasheet on potato tuber moth in the Plantwise knowledge bank.