Measure category: limit propagule pressure

Measures in this category include:

• Limit trade volume
• Limit consignment or packaging size
• Prevent escapes

Note that this resource is a working draft, which is currently being reviewed and updated in collaboration with biosecurity specialists.

Overview of measure category

Limit propagule pressure and thereby the likelihood that sufficient pests, if they were present and alive in the traded commodity, will escape to establish. Total propagule pressure is determined by trade volume, but propagule pressure at a potential establishment site will also be influenced by consignment and packaging size, and by measures to prevent escape. The relationship between propagule pressure and establishment risk is intimately linked with how the commodity will be used and the suitability of the destination habitat for establishment.

Required proof of efficacy

Demonstrate the relationship between actions to limit propagule pressure with establishment likelihood, taking into account relevant supply chain, biological (e.g. Allee effects) and environmental factors. Can also be supported through modelling (e.g. Jeger et al. 2018; Jamieson et al. in prep.).

How the measures are certified

Measures are primarily physical (e.g. trade volumes, packaging) so are readily auditable. 

How the measures are used

Measures to limit propagule pressure are rarely explicitly stated in trade protocols. However, they do contribute to PRA, including through quantitative pathway risk models developed by Jeger et al. 2018 and Jamieson et al. (in prep.) [check]. As phytosanitary measures they are most commonly associated with produce that undergoes further processing within the importing country, or for special-use products (such as introduction of live plants for scientific purposes).

Relationship with other measures

These measures are closely associated with measures that affect the destination and use of the commodity. If propagule pressure is demonstrably small then there may be less demand for other requirements, for example to reduce infestation rates in the consignment.

Consignment stages where the measures can be applied

Measures	Production	Post-production	Post-border
Limit trade volume	No	No	Yes
Limit consignment or packaging size	No	No	Yes
Prevent escapes	No	No	Yes

Measures in detail: limit propagule pressure

Measure	Required proof of efficacy	How the measure is certified	How the measure is used	Relationship to other measures
Trade volume Trade volume restricted to reduce the total number of pests that could enter.	Relationship needs to be determined between total propagule pressure (e.g. pests per year) and establishment risk.	(Requires further consideration)	An important consideration in a PRA. Trade volume may be restricted for a range of commercial and trade reasons. Although it has been suggested as a way of limiting biosecurity risks, we found no examples of trade volume restrictions being explicitly used to limit biosecurity risks. It may be a consideration for the import of material for scientific purposes.	Trade volume can be a consideration when setting entry requirements.
Consignment and packaging size Consignment size, or how the commodity is packed within the consignment, specified to limit the number of pests that may be released at any one time or place.	Relationship needs to be determined between total consignment and packaging size and establishment risk. Risk will also be affected by the nature of the supply chain and how the commodity is ultimately used.	Consignment and packaging size is readily auditable.	Will be relevant to PRA for some commodities where there is discretion on the size of the consignment and how it is packed, and pests where establishment risk is most sensitive to propagule pressure. We found no attempts to quantify the relationship between consignment and packaging size and establishment risk, and no examples of it being applied as a phytosanitary measure.	Relates to trade volume when estimating establishment risks.
Prevent escapes Actions specifically aimed at reducing the risk of pests escape within the importing jurisdiction.	HACCP can be used to identify points of risk through the supply chain. Measures are often established biologically (e.g. to establish required pore sizes or commodity segregation requirements under storage conditions). In some cases, experimental studies may be needed to establish the level of risk, and the efficacy of specific measures under commercial conditions.	Audit of physical barriers and processes.	Can include requirements relating to type of packaging, type of transport, speed of transport, time in post-shipping storage and packaging.	Similar to some pest exclusion measures but is focussed on inclusion of the pest rather than exclusion. Generally used in associated with other requirements such restricted use or processing requirements.

Key references

• Key references will be determined through consultation with biosecurity specialists and added here in the coming months.