Designing cost‐efficient surveillance for early detection and control of multiple biological invaders

Abstract

Wood borers and bark beetles are among the most serious forest pests worldwide. Many such species have become successful invaders, often causing substantial, costly damages to forests. Here we design and evaluate the cost‐efficiency of a trap‐based surveillance program for early detection of wood borers and bark beetles at risk of establishing in New Zealand. Although costly, a surveillance program could lead to earlier detection of newly established forest pests, thereby increasing the likelihood of successful eradication and reducing control costs and damages from future invasions. We develop a mechanistic bioeconomic model that relates surveillance intensity (i.e., trap density) and invasion size to probabilities of detection and control. It captures the dynamics of invasive species establishment, spread, and damages to urban and plantation forests. We employ the model to design surveillance programs that provide the greatest net present benefits. Our findings suggest that implementing a surveillance trapping program for invasive wood borers and bark beetles would provide positive net benefits under all scenarios considered. The economically optimal trapping strategy calls for a very high investment in surveillance: about 10 000 traps in each year of the 30‐year surveillance program, at a present value cost of US$54 million. This strategy provides a 39% reduction in costs compared with no surveillance, corresponding to an expected net present benefit of approximately US$300 million. Although surveillance may provide the greatest net benefits when implemented at relatively high levels, our findings also show that even low levels of surveillance are worthwhile: the economic benefits from surveillance more than offset the rising costs associated with increasing trapping density. Our results also show that the cost‐efficiency of surveillance varies across target regions because of differences in pest introduction and damage accumulation rates across locales, with greater surveillance warranted in areas closer to at‐risk, high‐value resources and in areas that receive more imported goods that serve as an invasion pathway.

Economics of invasive species policy and management

“…For example, beneficiaries of imported goods often are not the same entities that incur costs from invasions resulting from those imports (Lovett et al 2016). A forest owners association evaluating implementation of an early detection surveillance system for new invaders may not take into account the benefits of that system to city dwellers whose urban trees also would benefit from the system (Epanchin-Niell et al 2014). Landowners whose forestlands are being decimated by an invasive pest likely will not fully account for the benefits of their management for other forest owners when determining how much to invest in invasion mitigation, and therefore they may control less than is socially desirable (Aadland et al 2015).…”

“…Each subsequent study has typically relaxed assumptions of previous studies to increase the realism and applicability of the modeling approach for designing surveillance in specific systems. Some have focused on early detection of forest invaders, including brown treesnake (Boiga irregularis) (Kaiser and Burnett 2010), gypsy moth (Lymantria dispar) Bogich et al 2008;Berec et al 2015;Holden et al 2016), wood borer and bark beetles (Epanchin-Niell et al 2014), emerald ash borer (Yemshanov et al 2015), and oak wilt (Horie et al 2013).…”

“…They generally have found that implementing well-designed survey programs can substantially reduce costs. For example, Epanchin-Niell et al (2014) found that implementing an optimized trapping program for wood borers and bark beetles in New Zealand could reduce long-term costs by 40% relative to the absence of such a program. The existing body of research provides useful frameworks for designing cost-effective surveillance systems for detecting new invasions, as well as qualitative guidance identifying when surveillance is most worthwhile.…”

“…Specifically, greater investments in surveillance generally are warranted when establishment rates are high, expected invasion damages are high, and surveillance is less costly. For example, surveys targeting new incursions of wood borers and bark beetles are likely to provide the biggest bang for the buck when they focus more effort in areas that receive high amounts of imports associated with wood packaging material and are located near high-value, at-risk resources (Epanchin-Niell et al 2014). Also, when designing long-term surveys, greater survey effort may be warranted at the start of a program than later in the program if invader establishment rates are relatively low (Holden et al 2016).…”

“…This has been incorporated into some optimal surveillance work by simply assuming that a population of an established pest will be detected after some time period on the landscape if not detected by a trap (Epanchin-Niell et al 2014). However, Cacho and Hester (2011) and Cacho et al (2010) have explicitly evaluated the importance of passive surveillance in weed detection and eradication efforts and have shown how this can greatly reduce program costs.…”