Charting pest rankings: a concert of challenges

Like rockstars, roadies, fans and promoters congregating at a concert to feast on the music and money, groups of plant pests with shared appetites can also be found gathered at common venues.

CSIRO entomologist and CRC for National Plant Biosecurity researcher Dr Dean Paini calls these pest groupings ‘assemblages’. He uses the concept of selforganising maps to identify pest groupings that affect Australian agriculture and the environment. By identifying those pests currently absent from these groupings in Australia, but present in similar groupings overseas, he determines the pests that are most likely to establish here.

“If 10 species have established in a particular region, and nine of the same species have established in another region with a similar environment, then the likelihood of the tenth species establishing in the second region is very high,” he says, “like the ticket scalpers finally arriving on the concert stadium steps.”

His research has matched assemblages of 844 plant pathogens and insect pests across 459 different geographic zones around the world. Most regions represent either a country or, for larger nations such as Australia, the United States, China and Canada, the various states or provinces that make up that country. Every species was given a risk rating, on a scale of zero to one, according to how likely it was to establish in Australia based on the mapping of pest assemblages.

“All around the world biosecurity departments are looking for this kind of information to help them prioritise risk and allocate resources where they will be most effective,” he says. “This is an objective, analytical tool that can be used to support expert knowledge.”

Dr Paini says identifying whether a pest is likely to establish in Australia is only part of the risk-assessment equation. Other elements include the likelihood of a pest actually arriving and the potential cost to industry and to the Australian environment of an exotic pest incursion.

Not everything that makes its way to Australia will find favourable conditions and not every exotic pest will have a significant impact on industry, even if it does establish itself here.

Among the highest-ranked pests in Dr Paini’s mapping analysis were the yellow stem borer and the purple stem borer, both pests of rice crops, with risk indexes (out of one) of 0.7924 and 0.7722 respectively.

However, the comparatively small size of the Australian rice industry suggests that even should these pests establish here, the impact on the domestic economy would be relatively small.

The same cannot be said of the oriental fruit fly (Bactrocera dorsalis). Although it ranked 31st in Dr Paini’s research, with a risk index of 0.5008, it has the capacity to attack a wide range of fruit and horticultural crops. Complementary CRC risk-related research led by CSIRO economist Dr David Cook has identified potential costs of almost $652 million to the apple and pear industries alone, over 30 years, associated with an incursion of this pest.

Dr Cook’s research team has developed an enhanced risk-analysis model to assess the potential cost impacts of incursions and to help industry groups prioritise risks and areas for biosecurity investment.

Apple and Pear Australia Ltd (APAL) was among a number of horticultural groups that took part in Dr Cook’s research.

APAL general manager Tony Russell says the industry has had a long interest in biosecurity issues, crystallised by the potential of New Zealand apple imports bringing fire blight into Australia. Dr Cook modelled the impact for a range of pests nominated by APAL and fire blight was the pest with the highest impact, with an outbreak estimated to cost $846 million over 30 years.

“The modelling has provided us with an economic assessment, which helps to start the process of prioritising pests and making decisions about investment required,” Mr Russell says.

“The next phase will be the ability to model the spread of an incursion under different circumstances. To do that we realise we need better information about where our commercial orchards are located – so that we can better plan and respond to an incursion.”

Other horticultural groups that took part in the project, as members of Horticulture Australia Ltd, included the potato and vegetable industries, along with the Rural Industries Research and Development Corporation.

Dr Cook says an important part of the modelling project was actually gathering detailed information about the pests involved, which was collated into threat data sheets. Based at the Department of Agriculture and Food, Western Australia, Dr Abu-Baker Siddique spent three years collating detailed information about the 69 nominated exotic pests affecting 13 different horticultural industries involved in the project.

The data sheets include valuable specialist knowledge gathered from around the world, such as information on the different control and treatment regimes. They have provided essential information to the modellers developing the risk management tool.

The modelling produces statistical information about the likely economic impact of the nominated pests over a 30-year period. It takes into account control costs, loss of production and lost markets. When combined with a deliberative multicriteria evaluation (DMCE) framework, it includes an allowance for environmental and social costs of pests. For instance, where a pest has the potential to affect native flora and fauna, the implications of this damage can be compared with the agricultural damage to get a much clearer picture of the threat posed to Australia.

The tools developed by Dr Cook’s team allow industry and government participants to determine the trade-offs they may be willing to make in terms of allocating resources and potential impacts of an incursion. They also provide information that can be used to inform biosecurity policy decisions and establish cost-sharing arrangements for control measures.

“We found, when we began using the tools with stakeholders, that they were extremely interested in the assumptions and calculations used in putting the modelling together,” Dr Cook says. “But the model we had developed was extremely complex and it wasn’t easy to ‘crack it open’ to demonstrate the variables and how they influenced the outputs of the model.”

That’s one of the reasons for his next project – ‘Communicating uncertainty in biosecurity adaptation’. Dr Cook says it’s about developing a simpler form of the model that can be more easily understood and manipulated by non-modellers.

“I call it the ‘war games’ version. We’re planning to develop it as PC-based software that, with some training, industry groups will be able to use to try out different incursion and impact scenarios to help with their decision-making. It will have a map-based interface, which should be easier to use than the statistical outputs of the original model.”

Dr Paini is also moving on to a new risk-analysis project to identify the potential pathways for incursions into Australia – the ‘likelihood of arrival’ part of the risk equation.

He is specifically looking at indirect shipping connections that could bring high-priority pests to Australia. The project, ‘Six degrees of preparation’, is founded on network theory, well known in public health circles for studying the transfer of disease, such as the pandemics of SARS in 2002 and H1N1 influenza in 2009.

“You have to be able to identify what may be only a single link between two otherwise unconnected communities,” Dr Paini says. “For instance, goods coming from the United Kingdom could be transferred to containers from Asian countries that have previously carried grain infested with a pest that’s not commonly found in the UK, and that is not found in Australia. Those goods are then delivered to Australia and before long a bug crawls out of the woodwork and we have an exotic incursion on our hands.”