A simulation technology approach to Bactrocera spp: lessons from a past incursion for improving future responses

The Tephritidae family, and particularly Bactrocera spp., rank highly in economic importance for the AUD$6.9 billion Australian horticultural industry. The major species in this group is Bactrocera tryoni, known as Queensland fruit fly (Qfly), which is the major pest of horticulture in eastern Australia. The Qfly is highly polyphagous and is also multivoltine, being able to exploit fruit and vegetables all year round. Increasing interstate trade and tourism, and therefore the movement of people and tourism will encourage the transport of commodities that are a fruit fly risk. This increases the long-distance dispersal, and thus the risk of incursion of Qfly into new areas. Qfly is native to Australia and was originally only found in tropical and subtropical rainforests of Queensland. It has now been found from Victoria to far north of Queensland and in New South Wales, but is absent from WA, where it is considered to be a high impact pest species. Qfly has hundreds of hosts, including most tropical and temperate commercial fruits and vegetables. Potential losses to the threatened horticultural industry have been estimated at AUD$100 million a year, most attributable to Qfly.

In 1989, WA had its first incursion of Qfly and it spread rapidly throughout the Perth area. Although Qfly was eradicated, the historical event provided excellent data to allow a model of spread to be developed. Fruit surveillance at the time indicated that Perth had plenty of suitable fruit hosts available for Qfly and that the potential geographic distribution of B. tryoni would not be limited by temperature and rainfall. The Qfly flight range varies and its dispersal distance is debatable. The adults of Qfly are strong fliers but, in reality, most dispersal is over short distances within habitats, nevertheless, they can disperse between habitats separated by distances up to at least 90 km. Host availability for Qfly is a factor in determining dispersal flights between habitats. Clearly there is a need for an elegant approach to estimate and predict the worst case scenario for spread following an incursion. Such an approach will allow managers to simulate and predict the spread of any Bactrocera spp.

In this simulation project, we are focusing on population growth, time, host quality, seasonality, means of spread and the speed of spread of Bactrocera spp. after it is detected in a new habitat. Through the development of a simulator, rapid response and the selection a management strategy for containment/eradication can be developed. This project is developing methods for designing optimal surveillance strategies that quantitatively account for these factors. The product is a computer simulation model that provides decision-makers with more timely information to make decisions. The model has applicability for all levels of government within Australia allowing a national approach to any incursion. This simulation model has the potential to analyse and map many features of an eradication program.