Overview
Trade is restricted to commodities that are not hosts or carriers, or those hosts or carriers that are less vulnerable to infestation.
- Examples include limiting trade to non-host or less vulnerable fruit and vegetable species or cultivars, and to wood from tree species that are less likely to become infested.
- Evaluating the efficacy of this measure requires demonstrating that the most vulnerable developmental or quality stages of the commodity that are likely to be traded are poor or non-hosts or carriers when naturally exposed to the pest.
- The vulnerability of a commodity to infestation is a key consideration when conducting a pest risk assessment, with non-hosts not needing phytosanitary import requirements. Restricting trade to hosts or carriers that are less vulnerable or susceptible to infestation can be considered as a phytosanitary measure, including as part of a phytosanitary systems approach.
- For assurance, pre-border consignment inspection by authorised personnel, with oversight by the NPPO or relevant authority of the exporting jurisdiction, can ensure that only permitted commodities are being traded.
Evidence to support efficacy
In this measure, the vulnerability of the commodity to being a host or carrier is assessed for developmental or quality stages that are likely to be traded. Vulnerability can be described as a relationship between pest exposure and infestation rate. A non-host (or carrier) will not become infested even under high pest exposure rates whereas a vulnerable host may be infested even when pest exposure is relatively low. To be a host, a commodity must be able to be infested, and subsequently support the survival and development of the pest sufficiently to allow establishment to occur (host suitability). Likewise, to be a carrier, the commodity must be able to carry and retain live pests.
Field surveys can be used to assess the vulnerability of a commodity to be being infested. However, pest exposure rates, and the quality and developmental status of the commodity, need to be known and to be representative. To achieve this, surveys may need to be conducted over an extended period and under diverse conditions. For example, fruit infestation rates may need to be estimated throughout the season as the fruit matures, and from sites with different levels of pest prevalence.
No-choice laboratory studies are commonly used to determine whether a host can become infested/infected, and whether it can support the complete development of the pest. However, the vulnerability of a host can be overestimated in the laboratory. For example, some insect species that are known to be host specialists can lay indiscriminately in the laboratory, and pest development may differ in picked versus unpicked fruit. Semi-natural studies can address some of these limitations for some pests. For example, caged or sleeved field studies, and choice and no-choice greenhouse studies. In practice, a combination of field and laboratory studies may be necessary.
The comprehensiveness of the study, including sample sizes, will depend on the objective. Large sample sizes may be needed to demonstrate non-host status to high-risk pests. Comparative studies that include known preferred hosts may be needed when assessing whether a commodity is a poor-host or carrier.
The physiological status of the pest being tested also needs to be considered. This includes sexual maturity and prior exposure to hosts (in the case of insects that lay eggs into the host).
Applying the measure
How it is used
The vulnerability of a commodity to being infested is a key consideration when estimating unrestricted risk in a pest risk assessment and evaluating risk management options for a specific combination of commodity and pest. Phytosanitary import requirements are not needed if the commodity is a non-host (or non-carrier). In some cases, demonstrating that a commodity is a poor host or carrier may be sufficient to address the phytosanitary risk, or to reduce the requirement for additional measures. Thus, import requirements for the same pest may differ between host commodities depending on whether it is non-host, poor host or good host.
In some cases, a commodity may include more than one plant species or cultivar. If these differ in their vulnerability then this might result in only less vulnerable hosts or carriers being permitted, or less stringent import requirements and post-border inspection regimes being required for those. For example, fruit cultivars that are more resistant to a pathogen or less vulnerable to pest insects may be permitted for trade, as might timber from tree species that are less vulnerable to post-harvest timber pests and nursery plant seeds that are less vulnerable to disease. Similarly, high-risk carriers of invasive ants that are more likely to provide nesting spaces (such as soil) can be prioritised for regulation.
Use with other measures
Non-host (“conditional non-host”, RSPM 4) or non-carrier status does not need additional phytosanitary measures.
Where a commodity is a relatively poor host or carrier, but not sufficiently so to reduce risk to an acceptable level, it can be combined with other measures within a phytosanitary systems approach. This commonly includes Area of Low pest Prevalence or Low Pest Prevalence Site measures, and measures to reduce infestation rates (e.g. surface cleaning, remove contaminants). Phytosanitary import requirements may be less stringent than what is required for preferred hosts, if supported with sufficient evidence.
Similar measures
Developmental stage and quality specifications are closely related to, and sometimes considered as a component of, host or carrier.
Assurance of correct implementation
Assurance is required that only the permitted commodity or carrier is being traded. This can be achieved through pre-export inspection and phytosanitary certification by authorised personnel, with oversight by the NPPO or relevant authority of the exporting jurisdiction, confirming that only the approved variety or cultivar is exported.
References
The Asia and Pacific Plant Protection Commission (APPPC), 2005. Regional Standards for Phytosanitary Measures (RSPM) 04. Guidelines for the confirmation of non-host status of fruit and vegetables to Tephritid fruit flies. Food and Agriculture Organization of the United Nations Regional Office for Asia and the Pacific, Bangkok, Thailand.