Risk analysis of the invasion pathway of the Asian gypsy moth: a known forest invader

Abstract

Risk is defined with many minor variations in the biological literature. Common to most definitions are the following elements: the probability of a future event; and the consequences of the event, usually with respect to some predefined human value. Risk analysis includes elements of risk assessment (quantification of risk), uncertainty (of the event and its consequences), risk management (reducing risk to an acceptable level), and development of policy to balance finite resources with uncertainty and risk tolerance. When biological invasion and its risk are jointly examined, it is common that the consequences of invasion are not explicitly quantified, but understood to be sufficiently negative that it must be minimized to the extent possible. Risk analysis then becomes quantification of the probabilities of an introduction (event) and that the introduction leads to establishment, and the uncertainty of those probabilities. I describe a risk analysis framework for the Asian gypsy moth—a known invader—in its pathway. The framework uses the available information regarding the transportation route of the vector (ships), and a phenology model that estimates vector contamination (propagule size), the probability of introduction, and the probability of initial establishment given an introduction. Reducing propagule pressure is arguably the most important factor in reducing biological invasion; propagule pressure can be reduced by inspection and sanitation of the pathway vector (e.g., ships, trucks, humans) at the point(s) of departure and at the point of entry. I demonstrate how the risk analysis framework can be used to more efficiently target incoming ships for inspection and propagule pressure reduction.