Modelling the risk of importing pests in consignments of imported fruit

South Africa has to import fruit, which exposes the country to the possibility of acquiring unwanted pests and diseases. The object of the project was to model this risk so that steps to minimise it can be put in place. Cryptic pests can enter the country in large numbers. Therefore, in the case of these cryptic pests further procedures, such as cutting open fruit should be employed. In addition the quality of the inspections also influences the probability of detection, emphasising the need for highly trained and competent inspectors.

After importation, batches of not more that 30 kg of fruit are dispatched to supermarkets throughout the country. At infestation levels of up to 0.2%, the mean percent infested batches and the number of infested fruit arriving at supermarkets is zero. At infestation levels of between 0.3% and 2% the percent infested batches increases to almost 100%, but the number of infested fruit per batch remains low. At infestation levels above 2%, 100% of the batches will be infested and the number of infested fruit increases in proportion to the percent infestation.

In countries with similar apple pest assemblages to South Africa there are 79 pests which do not occur in South Africa. These are the pests with a high probability of establishment if they enter the country. Of these 79 pests 28 have a low to high probability of entering the country if apples are imported from regions in which they occur. Nineteen of these 28 pests also occur in other apple producing regions. The apple producing regions in which the most of these pests occur are in Western and Northern Europe and the regions in which the least occur are in China.