Measures in detail: Poor host or carrier

Measure	Required proof of efficacy	How the measure is certified	How the measure is used	Relationship to other measures
Poor host or carrier status Only commodities (cultivars, varieties, types) that are less vulnerable to infestation are permitted to be traded	Determining host or carrier vulnerability needs to consider the effect of pest abundance and to include the most susceptible stages or quality classes of the commodity that are likely to be exported. Conservative no-choice experiments can generally be conducted in the laboratory but results ultimately require testing under field conditions. Methods will depend on the organism. For example, insects can express learning and conditioning behaviours and physiologies. Prior experience and the availability of alternative, more suitable hosts can therefore affect the result. Similarly, some pests will express natural oviposition behaviours in the laboratory whereas other will not. Depending on market access requirements, studies will need to consider both likelihood of infestation/ infection (and associated symptoms) and subsequent survival and development	Requires assurance that only the permitted commodity (cultivar, variety or type) is being traded.	Host or carrier status is used for estimating unrestricted risk. As a measure it is only relevant where vulnerability to infestation differs among types of product or carrier, and where it is possible to limit trade to the least vulnerable type. Mostly used for fruit, where varieties can differ in vulnerability to infestation. However, it may not be practical where a wide diversity of cultivars is grown and traded.	Poor host or carrier status can be combined with other measures, such as low pest prevalence or measures to reduce infestation rates.
Poor host developmental stage / poor host quality Trade is restricted to specific development stages that are least vulnerable as hosts or carriers.	As for poor host or carrier status, but with a focus on host developmental stage. Data needs to demonstrate that a clearly identifiable (and gradable) stage of the commodity is sufficiently less vulnerable to infestation than alternative stages when exposed under the same conditions.	Audits of processes (including grading, training) and of graded commodity.	Developmental stage can be considered during PRA for commodities where grading for the correct developmental stage is a commercial imperative (such as to optimise storage and shelf life). It is commonly applied to fruit that continue to mature after harvest, and where less mature stages are less vulnerable to infestation. It can also be relevant to other commodities such as timber and plants for planting. At its most extreme this is a conditional non-host.	Poor developmental stage is functionally similar to quality specifications of commodities. Both require grading, but poor developmental stage is most often imposed by regulators based on empirical evidence.
Quality specification Quality specifications applied to exclude commodity that are most likely to be infested. Quality is generally defined commercially based on factors such as degree of acceptable damage, health (of the plant) and ripeness.	Data is required to quantify the relationship between quality and infestation risk. This can be determined experimentally and through field survey (in-field and post-harvest). Evidence is also required to show that grading processes are sufficiently accurate. When stipulating specifications for grading care needs to be given to ensure that they can be readily applied by both workers and auditors, and that “false positives” that result in waste are minimised.	Audits of processes and of post-graded commodities against grading requirements.	Quality grading may significantly reduce infestation risks for pests and commodities, for example where poorer grade commodities are more vulnerable or have been exposed to the pest for longer. International exports generally focus on the sale of high-quality commodities, and there are industry-set quality standards for some commodities and markets. However, quality grading is not always considered during PRA, and is rarely specified as a phytosanitary measure. One reason may be the lack of data needed to quantify its benefits.	This measure is similar to poor developmental stage, but quality specifications are often determined by industry standards. A quality grading requirement is often combined with the symptom grading measure, but they reduce risk in very different ways, and different data to support efficacy is needed for each. Commodity is removed through quality grading irrespective of pest abundance (and infestation rate), whereas commodity removal through symptom grading will be proportional to infestation rate.
Modify vulnerability Modification of the physical or chemical properties of the commodity to make it less vulnerable to becoming infested	As for poor host stage or quality class but taking into account the effects of the intervention when applied under commercial conditions.	Audit of processes. The commodity could also be audited if the intervention remains detectable.	A range of methods are used to reduce the vulnerability of wood or wood products to subsequent infestation, for example kiln drying, wood chipping, water spraying, and removal of bark. Methods have been proposed for fruit, for example the use of spays such as copper or kaolin clay, but we found no examples of their use in practice.  Some post-production practices such as waxing might affect post-harvest infestation risks.	May be used as part of phytosanitary systems approach, or within a set of measures to prevent infestation of the commodity post-production.
Remove/prohibit parts of the host or carrier Removal or prohibition of parts of the host that are most likely to carry the pest.	Can be quantified experimentally using infested commodities and confirmed under a commercial setting. Needs to account for the biology of the pest.	Audit of treatment records and processes. Effects of measures may also be auditable.	Used in specific cases where the pest is largely restricted to parts of the commodity that can be readily removed. That may include debarking of timber (for beetle borers), removal of plants stems and leaves (for some fruits) and bare-rooting plants.	Can be combined with surface cleaning or symptom grading measures when the pest is not entirely restricted to the removed part.

Consignment stages where the measure can be applied

Measure	Production	Post-production	Post-border
Poor host or carrier status	Yes	Yes	No
Poor developmental stage	Yes	Yes	No
Quality specifications	Yes	Yes	No
Modify host vulnerability	Yes	Yes	No
Remove/prohibit parts of the host or carrier	Yes	Yes	No