Estimation of the probability of insect pest introduction through imported commodities

A quantitative risk assessment is needed for each quarantine pest insect to ensure quarantine security without sacrificing the transparency of international trade. The probability of introduction, which is defined as the probability that one or more reproductive individuals of a pest insect species pass the port, is one of the basic components determining the risk of pest invasion. The probability depends on two biological characteristics of pests: mode of reproduction and spatial distribution of insects per host plant. In this article, the probability of introduction was calculated for each of the following four categories: (1) bisexual, gregarious pests; (2) bisexual, solitary pests; (3) parthenogenetic, gregarious pests; and (4) parthenogenetic, solitary pests. Then, equations were derived to predict the effects of two prevention practices conducted before export: disinfestation treatment and the subsequent export sampling inspection of consignments. These equations also enable estimation of the probability of introduction under natural mortality, which thus can be used in place of the criterion of Maximum Pest Limit (MPL). The method was applied to the Mexican fruit fly Anastrepha ludens (Loew), as an example. The contour graph of the probability of introduction indicated the optimal combination of the intensity of two prevention practices that ensures a given security level. Existence of an antagonistic interaction was also indicated between the disinfestation treatment and the subsequent sampling inspection. Received: January 22, 1999 / Accepted: September 6, 1999