FORUM Eradication of Invasive Species: Why the Biology Matters 1,2,3 2,4 ANDREW PAUL GUTIERREZ AND LUIGI PONTI Environ. Entomol. 42(3): 395Ð411 (2013); DOI: http://dx.doi.org/10.1603/EN12018 ABSTRACT Published bi- and tri-trophic physiologically based demographic system models having similar sub components are used to assess prospectively the geographic distributions and relative abundance (a measure of invasiveness) of six invasive herbivorous insect species across the United States and Mexico. The plant hosts and insect species included in the study are: 1) cotton/pink bollworm, 2) a fruit tree host/Mediterranean fruit ßy, 3) olive/olive ßy, 4) a perennial host/light brown apple moth, 5) grapevine/glassy-winged sharpshooter and its two egg parasitoids, and 6) grapevine/European grapevine moth. All of these species are currently or have been targets for eradication. The goal of the analyses is to predict and explain prospectively the disparate distributions of the six species as a basis for examining eradication or containment efforts against them. The eradication of the new world screwworm is also reviewed in the discussion section because of its pivotal role in the development of the eradication paradigm. The models used are mechanistic descriptions of the weather driven biology of the species. Observed daily weather data (i.e., maxÐmin temperatures, solar radiation) from 1,221 locations across the United States and Mexico for the period 1983Ð2003 were used to drive the models. Soil moisture and nutrition were assumed nonlimiting. The simulation results were mapped using GRASS GIS. The mathematical underpinnings of the modeling approach are reviewed in the appendix and in the supplemental materials. KEY WORDS light brown apple moth, fruit ßies, pink bollworm, glassy winged sharpshooter, European grapevine moth We’re in the middle of an eradication program pesticides, pheromones, cultural practices, quarantine, and can’t afford the luxury of research. and combinations including applications of biotechnol- ÑA “high USDA ofÞcial” quoted by Paul ogy (Robinson 2002) have been used in eradication or Ehrlich (see Burk and Calkins 1983). containment efforts. However, despite years of effort and expenditures of hundreds of millions of dollars, many How would you make recommendations for con- invasive species problems remain unresolved. trol of an invasive species in the absence of infor- In this article we examine prospectively the effects mation? of weather on the distribution and relative abundance ÑQuestion to A.P. Gutierrez from an invasive (invasiveness) of six invasive herbivorous insect spe- species scientist, USDA/APHIS/PPQ, Raleigh, cies across the United States and Mexico, and use the NC. results to examine the eradication or containment efforts against them. We use published weather- Invasive species may be of any taxa, and collectively driven, physiologically based demographic models are estimated to cause in excess of $140 billion in losses (PBDMs) developed by us and our colleagues in this annually in the United States (Pimentel et al. 2005) effort. and a trillion worldwide (Oerke and Dehne 2004). The host/insect systems in our study are: 1) cot- Eradication of an invasive species may be desirable but ton (Gossypium hirsutum L.)/pink bollworm (Pecti- elusive, and need not be attempted in some cases (see nophora gossypiella (Saunders)) (Gutierrez et al. Myers et al. 1998, 2000). The sterile insect technique 2006b); 2) a fruit tree host/Mediterranean fruit ßy (SIT) (Knipling 1955), and other methods including (medßy, Ceratitis capitata (Wiedemann)) (Gutierrez and Ponti 2011); 3) olive (Olea europaea L.)/olive ßy (Bactrocera oleae (Rossi)) (Gutierrez et al. 2006c, 1 Division of Ecosystem Science, College of Natural Resources, 2009; Ponti et al. 2009a, b); 4) grapevine (Vitis vinifera University of California, Berkeley, CA 94720-3114. 2 Center for the Analysis of Sustainable Agricultural Systems (CA- L.)/glassy-winged sharpshooter (Homalodisca vitripen- SAS Global), 37 Arlington Ave., Kensington, CA 94707. nis (Germar))/two egg parasitoids (Wermelinger et al. 3 Corresponding author, e-mail: [email protected]. 1991, Gutierrez et al. 2011); 5) a perennial host plant/ 4 Laboratorio Gestione Sostenibile degli Agro-Ecosistemi (UTAGRI- light brown apple moth (Epiphyas postvittana (Walker)) ECO), Agenzia nazionale per le nuove tecnologie, lÕenergia e lo sviluppo economico sostenibile (ENEA), Centro Ricerche Casaccia, Via Anguil- (Gutierrez et al. 2010a); 6) grapevine/European grape- larese 301, 00123 Roma, Italy. vine moth (Lobesia botrana (Denis and Schiffermu¨ller)) 0046-225X/13/0395Ð0411$04.00/0 ᭧ 2013 Entomological Society of America 396 ENVIRONMENTAL ENTOMOLOGY Vol. 42, no. 3 (Gutierrez et al. 2012). Because of the pivotal role the Appendix). PBDMs capture mechanistically the biol- native new world screwworm (Cochliomyia hominivorax ogy of species in response to weather and trophic (Coquerel)) played in the development of the eradica- interactions independent of species distribution data. tion paradigm, its eradication in the United States, Mex- Tri-trophic PBDM systems may include bottom-up ico, and Libya is reviewed in the discussion section effects on phenology, growth and development of (Gutierrez and Ponti in press). The extensive literature whole plants and plant subunits (e.g., fruits, leaves, and the basic mathematical structure underpinning the etc.); the relevant biology and dynamics of herbivo- models are outlined in the cited articles, while the gen- rous species feeding on them; and as required the eral form of the physiologically based demographic mod- top-down action of natural enemies (e.g., Gutierrez els (PBDMs) common to all of the species is reviewed in and Baumga¨rtner 1984, Gutierrez et al. 1994). Con- the Appendix and the Supplemental Materials. sumer species affect the dynamics of the resource Central to the analysis of the distribution and abun- species and vice versa. The tri-trophic grapevine/ dance of heterotherm species is the inßuences of glassy-winged sharpshooter/parasitoid system model weather and climate (e.g., Andrewartha and Birch provides a good overview of the PBDM approach 1954). Climate is the long-run pattern of meteorolog- (Gutierrez et al. 2011). ical factors (e.g., temperatures, rainfall, etc.) in a given With variations, the PBDM approach to modeling location or larger region, while the term weather re- plant growth and development is well established in fers to short-run measures of these factors. The biol- the literature (see Marcelis and Heuvelink 2007, ogy of heterotherm species evolves in response to Rodrõ´guez et al. 2011). PBDMs for plants consist of age climate, interacting species, and other factors in the and mass structured subunit population dynamics native range that in total deÞne its ecological niche models linked via photosynthate availability that gov- (see van der Putten et al. 2010). This biology deter- erns growth and development of extant subunits and mines a speciesÕ temporal and spatial dynamics and geo- the production of new ones. Photosynthesis is esti- graphic range, and the potential areas it may invade. mated using a functional response model (predator Weather (e.g., daily) affects heterotherm physiology, form) driven by current age structured assimilation behavior, interactions with other species, and hence the demands, leaf area index, light, temperature, and other dynamics of the species in current time and place. factors (see Gutierrez et al. 2005, 2006b). We assumed nonlimiting water and nutrients in our analyses be- cause data on plant species root depth, soil moisture Modeling the Distribution and Abundance of holding capacity, and soil fertility on a continental Invasive Species scale were unavailable. This may lead to over predic- Several methods have been used to assess the geo- tion of plant distribution in arid areas (see Hickler et graphic distribution of heterotherm species. For per- al. 2009). A tri-trophic study of the noxious yellow spective, we contrast the commonly used ecological starthistle (Centaurea solstitialis L.) in California in- niche modeling (ENM) approach(s) and the PBDM cluded soil moisture and explained the failed biolog- approach used here. Each approach has strengths and ical control of the weed (Gutierrez et al. 2005). weaknesses. PBDMs for the insect species are also age-struc- ENM Approach. The ENM may be statistical, phys- tured but may have attributes of stage, mass, sex, dor- iological indices, or based on information theory (see mancy, behavior, and other factors as necessary. The Elith and Leathwick 2009). ENMs are relatively easy data required to formulate the models for each insect to implement and seek to characterize climatically the species are outlined in the Appendix (Figs. A1 and geographic range of a species based on aggregate A2). The herbivore models are driven primarily by weather data (and other factors) from areas of the temperature and the demand for and supply of pre- recorded distribution (Beaumont et al. 2009). ENMs ferred plant subunits. The acquisition biology of this are used to predict the potential native range of the and higher trophic levels is captured by the same species and prospectively its range in new areas. How- functional response model used for plant photosyn- ever, ENMs have implicit ecological and mathematical thesis, albeit with different units, and using either the assumptions that lack mechanistic biological under- predator or parasitoid forms as appropriate