The role of vector behaviour and competence on the spread of Cacao swollen shoot virus

Dr. Mandela Fernandez-Grandon, Natural Resources Institute, University of Greenwich
Dr. Gonçalo Silva, Natural Resources Institute, University of Greenwich
Dr Jean-Philippe Marelli, Mars Wrigley

project details

Cacao swollen shoot disease (CSSD) is devastating the production of cacao in West Africa and consequently trammelling socioeconomic development in the region and threatening global production of chocolate. The virus responsible, Cacao swollen shoot virus (CSSV, genus Badnavirus) is spread by mealybugs feeding on the cacao and is recognised as the causal agent of the most economically important disease in cacao, accounting for yield losses of between 15-50% (Ameyaw, 2019). An estimated 60% of all cacao is grown in Ghana and Cote d’Ivoire, with around 90% of all growers being small-hold farmers (Fairtrade Foundation, 2019). Currently these farmers implement a “cutting out” method to reduce virus spread. This is simply the removal of virus-infected plant material and those plants in the vicinity. This method is far from ideal for the farmer or ecosystem and is often rendered ineffective due to the late detection of the virus (Ameyaw, 2019). The increased land usage required to meet demand subsequently leads to expansion of cacao farms and damage to natural ecosystems or destruction of forested areas. To improve the livelihoods of those in the area and mitigate against environmental damage, the problems of cacao disease must be tackled.

Natural Resources Institute has a history of 125 years of research focussing on improving the livelihoods for those in low-income countries. For this PhD studentship we are partnering with Mars Wrigley to explore the problem of CSSD and novel approaches to its control.
As part of this exciting interdisciplinary project, the student will explore aspects of vector behaviour, competence in spreading the virus, and the chemical ecology associated with the system. This approach is focused around the three following broad objectives:

  • Identification of volatiles associated with CSSV infection
  • Testing the behavioural response of the vector to infected/non infected material
  • Molecular characterisation of the mealybugs present in infected fields and measuring the species/populations ability to transmit the virus.

Our hypotheses are that volatile profiles of Cacao sp. are altered by CSSV infection and that this change in volatile profile will affect vector behaviour. Both the change in volatile profile associated with viruses and modulation of the vector behaviour have previously been observed in numerous other systems (Ingwell et al., 2012; McMenemy et al., 2012; Fereres et al., 2016) This approach will give a more complete insight to the interactions involved. As important as it is to find out more about the vector, there is also a practical reason for this approach; new, more cost-effective diagnostic systems may be developed through identifying changes in the volatile profile associated with virus infection. We have conducted preliminary experiments to establish a technique for volatile collection, and recent work has shown plant disease diagnostics are viable through volatile sensors (Li et al., 2019). Identifying the volatiles present could open the door for alternative rapid, cheap and locally viable solutions such as the use of sniffer dogs which has shown success in similar environments for disease detection (Mendel et al., 2018).

Understanding the variance in vector competence will allow for more targeted control approaches reducing the damage to non-target species. Knowing which volatiles attract the vector will also provide opportunities for directly approaching control of the vector through trapping, something which has been called for repeatedly in the community.
Laboratory work in the UK will use our state-of-the-art electrophysiology, chemical analysis and molecular biology suites with training provided by the supervisory team. Field will work take place with partners in largest cocoa producing country, Cote d’Iviore. The student will also spend time on placement with partners at Mars Wrigley.


  • Fairtrade Foundation. 2019. Available from:
  • Ameyaw, G.A., 2019. Plant Pathology and Management of Plant Diseases.
  • Ingwell et al., 2012. Scientific Reports
  • McMenemy et al., 2012 Ent. Exp. Et Appl.
  • Fereres et al., 2016 Viruses
  • Li, Z., et al. 2019. Nature plants, p.1.
  • Mendel et al. 2018 HortTechnology, 28(2)

eligibility and application

Applicants must hold, or be expected to achieve, a first or high upper second-class undergraduate honours degree or equivalent (for example BA, BSc, MSci) or a Masters degree in a relevant subject. This project is funded by a 4-year BBSRC studentship, applicants should ensure they have understood the funding eligibility criteria for these studentships. Unfortunately international students are not eligible for programme funding on this project.

For more information regarding the project, please contact Dr. Mandela Fernández-Grandon

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