An agent-based simulation of extirpation of Ceratitis capitata applied to invasions in California

Nicholas C Manoukis,Kevin Hoffman

doi:10.1007/s10340-013-0513-y

Abstract

We present an agent-based simulation (ABS) of Ceratitis capitata (“Medfly”) developed for estimating the time to extirpation of this pest in areas where quarantines and eradication treatments were immediately imposed. We use the ABS, implemented in the program MED-FOES, to study seven different outbreaks that occurred in Southern California from 2008 to 2010. Results are compared with the length of intervention and quarantine imposed by the State, based on a linear developmental model (thermal unit accumulation, or “degree-day”). MED-FOES is a useful tool for invasive species managers as it incorporates more information from the known biology of the Medfly, and includes the important feature of being demographically explicit, providing significant improvements over simple degree-day calculations. While there was general agreement between the length of quarantine by degree-day and the time to extirpation indicated by MED-FOES, the ABS suggests that the margin of safety varies among cases and that in two cases the quarantine may have been excessively long. We also examined changes in the number of individuals over time in MED-FOES and conducted a sensitivity analysis for one of the outbreaks to explore the role of various input parameters on simulation outcomes. While our implementation of the ABS in this work is motivated by C. capitata and takes extirpation as a postulate, the simulation is very flexible and can be used to study a variety of questions on the invasion biology of pest insects and methods proposed to manage or eradicate such species.

Highlights

We present an agent-based simulation (ABS) of Ceratitis capitata (‘‘Medfly’’) developed for estimating the time to extirpation of this pest in areas where quarantines and eradication treatments were immediately imposed
Ceratitis capitata (Mediterranean fruit fly, ‘‘Medfly’’) is a major threat to agriculture around the world because it can infest a large variety of commercial fruit crops (Liquido et al 1990) and is able to persist in a wide variety of habitats (Messenger 1959)
We have developed and implemented in the program MED-FOES an ABS designed to test quarantine lengths following a find of C. capitata in an area where it is not established

Summary

Introduction

Ceratitis capitata (Mediterranean fruit fly, ‘‘Medfly’’) is a major threat to agriculture around the world because it can infest a large variety of commercial fruit crops (Liquido et al 1990) and is able to persist in a wide variety of habitats (Messenger 1959). We use an ABS implementation called MED-Fly Outbreak and Eradication Simulation (MEDFOES) to study the time to extirpation (local extinction) of C. capitata following seven actual detections of this pest that occurred in Southern California between 2008 and 2010 This is done through detailed modeling of individual flies and their life expectations based on probability density functions of survival, developmental rate, and reproductive potential determined from the actual population studies. Computer simulations of complex systems in biology are increasingly common, driven by rapid increases in processing speed, decreases in processing cost and complexity, and the realization that simulations can aid the researcher and program manager in considering added complexity of the real world, while freeing them from limitations imposed by analytical solutions of complex mathematical processes (Huston et al 1988) The latter is true for ABS models ( called ‘‘IndividualBased,’’ or ‘‘Multi-Agent’’ models), which can be minimally defined as simulations where individuals are described as unique and autonomous, and where they may interact with each other and their environment on a local level (Railsback and Grimm 2012).

Materials and methods

Design concepts

Results

Findings

Discussion