cesar research scientist and team lead, Dr Olivia Reynolds, has been leading an intrepid new project investigating the biology of a priority pest in the cocoa production industry of Papua New Guinea. With two research field trips to affected cocoa production areas complete, the project has begun to yield some promising results.
When I overheard that cesar Research Team Lead (and entomologist), Dr Olivia Reynolds, was on the hunt for livestock feed I was initially confused. Then realisation set in – it all comes down to a particular plant pest and biosecurity threat, the cocoa pod borer (Conopomorpha cramerella), and creating just the right mix of nutrients to sustain a colony outside of its common host plant.
As the name suggests, cocoa pod borer is a pest of cocoa. However, it also feed on tropical fruits, such as rambutan and longan. As a lepidopteran insect the cocoa pod borer develops from egg to caterpillar to pupa, before finally emerging as a small (approximately 7mm) adult moth. Notable production damage can be attributed to feeding of the caterpillar within the pod, which will cause premature or uneven ripening. The interruption of cocoa bean development causes the beans to clump together, making them difficult to be harvested and processed and reducing yield.
The cocoa pod borer is a pest throughout parts of South East Asia and the Western Pacific. As far back as the 1840’s the borer was attributed with the translocation of the North Sulawesi cocoa industry to the Philippines and Java (the North Sulawesi cocoa industry has since recovered) (Toxopeus & Giesberger, 1983). More recently, a cocoa pod borer outbreak in Papua New Guinea has placed farmers under pressure. Where recommended management steps have proved impractical, farmers have changed crops or opted to send cocoa pods to local markets.
“Cocoa plantations in Papua New Guinea tend to be largely small-holder family farms, and effectively managing this destructive pest has thrown up some challenges. Any change, or improvement to current pest management practices to combat the cocoa pod borer needs to be achievable and cost-effective” stresses Dr Reynolds.
Pinning down cocoa pod borer biology, ecology and behaviour is an important part of the research, which is funded through the Australian Centre for International Agricultural Research (ACIAR) and is a collaboration between cesar, New South Wales Department of Primary Industries, the University of Sydney, the Cocoa Board of Papua New Guinea, the South African Sugarcane Research Institute, Stellenbosch University and the United States Department of Agriculture.
The project has three major objectives:
- To review what research has been conducted to date on the pest, and identify the gaps in our knowledge on identification and management
- To resolve the identification of the cocoa pod borer (it is not known if the borers affecting cocoa production regions overseas are different species, or genetic variants of the same species)
- To determine the best method of culturing the pest in a laboratory environment (this explains the hunt for livestock feed)
With the first two field trips to Papua New Guinea completed during October 2018 and February 2019, the project is well underway. So, what has been found to date?
Let the DNA do the talking
After collecting over 150 samples of cocoa pod borer from three cocoa producing provinces of Papua New Guinea (as well as receiving international specimens), caterpillars, pupae and adults were received by project collaborators in New South Wales for taxonomic and molecular identification. Preliminary molecular analysis of a subset of data has detected two of the five known cocoa pod borer haplotypes, but also an additional, novel haplotype. Further, molecular results have identified another lepidopteran species infesting cocoa that was previously not known to be a pest of the crop!
As the research progresses, further molecular analysis will support development of a diagnostic that will enable accurate identification and will assist with painting a picture of how the cocoa pod borer has moved through Papua New Guinea (and further clarify if the pest was present before cocoa plantations entered PNG).
Finding the Goldilocks recipe
The ability to raise, or ‘culture’ a pest is extremely useful. Once a colony can be kept in a controlled laboratory environment more sophisticated research into the biology, behaviour and ecology of the pest can be carried out. Such further research is a crucial step in employing additional methods to combat the pest, such as the Sterile Insect Technique – a methodology that has been used in several Australian states to aid eradication of Queensland fruit fly in fruit fly free areas for decades.
The method in use to determine the best diet for cocoa pod borer is termed ‘the comparative slaughter technique’, which is also colourfully known as ‘the carcass milling technique’. This involves collecting caterpillars (after observing the hosts on which they have been feeding) and assessing their body compositions for dry matter, protein, fat, and key nutrients. Similarly, it also involves analysing the host material. These analyses can give scientists a template for developing the ideal diet.
Contributing to a community of interest
Importantly, the trip also allowed the research team to build knowledge about cocoa pod borer in affected areas as many farmers recognise the damage, but not what the pest looks like.
“Correct identification, of both the pest and damage, is the first essential step to good pest management. A community driven approach to learning more about this pest and its biology and ecology will be extremely important in effectively controlling the cocoa pod borer in Papua New Guinea,” says Dr Reynolds.
In turn, locals shared their observations about the pest damage they had observed.
Where to from here?
In countries that remain unaffected by the pest, surveillance remains a priority as the borer can travel long distance via infested fruit. Thus, this research has benefits for both our neighbours in cocoa pod borer affected nations including Papua New Guinea and for tropical fruit farmers in Australia through the development of a diagnostic protocol. We are the only agricultural nation in the world to have eradicated cocoa pod borer after it was detected in Queensland in 2011. Further, the development of an artificial diet will not only enable a greater understanding of the biology, behaviour and ecology of the pest under controlled conditions, but will allow the development of more sophisticated management techniques such as the sterile insect technique.
This research will continue with another visit to the PNG Cocoa Board entomology laboratory in June, where further activities will include testing the fitness and performance of the cocoa pod borer on eight diets developed using the comparative slaughter technique.
With all this talk of cocoa, you must ready for a treat or two… try sourcing single origin chocolate from PNG to try its distinctive fine flavour. After the completion of this third research mission we will have further pieces of the cocoa pod borer puzzle to share.
Until then, good-bye, Lukim yu, choco-later!
This research is funded by theAustralian Centre for International Agricultural Research (ACIAR). Project partners are the New South Wales Department of Primary Industries, the University of Sydney, the University of Stellenbosch, the South African Sugarcane Research Institute, and the Papua New Guinea Cocoa Board.