The major uncertainties encountered in this risk analysis are identified here. The assumptions made to take account of them are explicitly identified where relevant in the text.
6.1. Hazard biology and identification
• The biology of insects that have been reared in the laboratory for several generations is often different to wild counterparts established in field conditions (Mangan and Hallman 1998). Aspects such as life cycle, preovipositional period, fecundity and flight ability (Chambers 1977), as well as cold or heat tolerance can be influenced by the highly
controlled laboratory environment. Laboratory reared insects may differ in their responses to environmental stress and exhibit tolerances that are exaggerated or reduced when compared with wild relatives. For example longevity and fecundity of adult Aphis gossypii in a greenhouse was longer and higher than those in a growth chamber with similar conditions (Kim and Kim 2004).
• If a pest species occurs in New Zealand often its full host range or behaviour in the colonised environment remains patchy. It is difficult to predict how a species will behave in a new environment, particularly if it has not become established as a pest elsewhere outside its natural range. Therefore there will be considerable uncertainty around the likelihood of an organism colonising new hosts or the consequences of its establishment and spread on the natural environment. Where indigenous plants are discussed as potential hosts this is extrapolated from the host range (at genus and family level) overseas and is not intended as a definitive list.
• Where there is uncertainty about the identity of an organism, e.g. Prays citri vs P.
nephelomima, the more serious pest is considered in the RA. The conclusions may need to be revisited if evidence to the contrary becomes available.
• There is uncertainty around the efficacy of risk management measures for many of the hazards identified in this Risk Analysis. In some cases efficacy data for similar species has had to be used.
6.2. Assumption regarding transit time of fruit on the air pathway
An assumption is made around the time the fruit takes to get from the field in Samoa to New Zealand ready for wholesale if it is transported by aircarrier. It is assumed that the harvesting, treatment, packing and transit of Citrus fruit from Samoa, inspection and release in New Zealand will take a minimum of 24 hours, and on average will take 48 hours.
6.3. Assumption and uncertainty around disposal of infested fruit
It is not known what proportion of imported Citrus will be consumed or discarded.
It is assumed that a proportion of Citrus that is infested or damaged will be disposed of in a manner that exposes any potential hazard organisms on that fruit to suitable hosts. Disposal would include discarding fruit or peel on urban or rural roadsides, in bush reserves, in open rubbish bins in public places, and on open composts in domestic areas.
6.4. Assumption and uncertainty around risk management measures
A lot of uncertainty exists around the efficacy of risk management measures. Interception data is one way of estimating efficacy, as records of live and dead organisms indicate the success of a treatment and the thresholds for growth and development of each individual organism. A sample audit is required to monitor efficacy. Currently this is 600 units of fruit/vegetable product per consignment. The assumption is that this monitoring will adequately record type and number of organisms associated with each fresh produce commodity.
This approach makes the following assumptions, that:
• the consignment is homogeneous (fruit are harvested inspected and packaged in similar conditions, and have received similar treatments before arrival into New Zealand). Heterogeneous or non-randomly distributed consignments would require a higher sampling rate to achieve the same confidence levels. Level of sampling depends on the degree of heterogeneity;
• the samples are chosen randomly from the consignment;
• the inspector is 100 percent likely to detect the pest if it is present in the sample. Because of uncertain distribution of pests within the consignment some pests will not be detected if they are present outside the 600 unit sample. Some pests are difficult to detect because of their small size and behaviours;
• it is acceptable that the sampling system is based on a level (percentage) of contamination rather than a level of surviving individuals;
• because for lines of less than 600 units, 100 percent inspection is required, it is therefore acceptable that the effective level of confidence gained by the sampling method
significantly increases as the consignment size moves below 10,000. This is because a sample of around 590 provides 95 percent confidence that a contamination level of 1 in 200 (0.5 percent) will be detected in consignments larger than about 25,000 individuals. Interception records can rarely be used quantitatively because of limitations in the
identification and recording processes.
There is a paucity of information on the efficacy of the available risk mitigation options in managing the hazards associated with Citrus. In the absence of efficacy data, assumptions are made on the basis of data for similar species or similar treatments.
6.5. References
Chambers, D L (1977) Quality control in mass rearing. Annual Review of Entomology. 22: 289-308
Kim, Y H; Kim, J H (2004) Biological control of Aphis gossypii using barley banker plants in greenhouse grown oriental melon. Conference on Biological Control, Berkeley, California. 13-15 July 124-126pp
Mangan, R L; Hallman, G J (1998) Temperature treatments for quarantine security: new approaches for fresh commodities. Chapter 8 In: Hallman, G J; Denlinger, D L (Eds.) Temperature Sensitivities in Insects and Applications in Integrated Pest Management. Westview Press, Boulder, Colorado. Pp 201-236