Simulation Modelling as a Decision Support in Developing a Sterile Insect-Inherited Sterility Release Strategy forEldana saccharina(Lepidoptera: Pyralidae)

Abstract

A user-friendly simulation tool for determining the impact of the sterile insect technique/inherited sterility technique (SIT/IS) on populations of the African sugarcane stalk borer, Eldana saccharina Walker (Lepidoptera: Pyralidae) is described in this paper. The simulation tool is based on a spatio-temporal model. The design of the simulation tool is such that it is applicable for use in a number of pest/crop and pest control scenarios. It uses 4 interacting subsystems (pest species population dynamics, crop dynamics, environmental dynamics and economics) within a specified spatial domain. Furthermore, the spatial domain describes the layout of the agricultural crop (position, size, shape, crop age and variety of the different fields contained within the crop area). The pest species population subsystem describes E. saccharina population dynamics (but is designed to also include population dynamics of other pest species) under the influence of the IS technique. The E. saccharina module developed utilizes mean-field and spatio-temporal models, and includes dynamics of all E. saccharina life stages under the influence of the control measure. Only temperature and damage caused by E. saccharina are currently included as variables in the sugarcane dynamics subsystem. This subsystem estimates stalk length as a function of time and temperature, and sucrose percentage as a function of damage caused by E. saccharina boring. Interaction between E. saccharina population growth and sugarcane growth is described by a decreasing s-shaped density-dependent mortality function-the older the cane, the higher the carrying capacity (more food resources) and corresponding infestation and damage levels. The only environmental factor considered as an independent variable in the environmental dynamics subsystem is temperature. Possible extensions to this subsystem are discussed. The economics subsystem developed includes the estimation of the recoverable value, percentage, expected revenue and the cost of control. No other farm expenditures are taken into account. As such only profit or loss expected from applying the IS technique is estimated. The profit or loss is defined as the increase in revenue expected less the cost of applying a pest control measure. An example of using the simulation tool is presented in the context of a real field scenario of a simulated SIT/IS program against E. saccharina at a pilot site near the Eston area of KwaZulu-Natal, South Africa.

An agent‐based simulation model of Eldana saccharina Walker

“…This consisted of an accompanying SIT simulation tool whereby the effectiveness of SIT can be investigated in different scenarios. Potgieter et al (2016) then presented a high-level design of a simulation tool for investigating different IPM strategies against E. saccharina in sugarcane which may be extended to incorporate other species. This design consisted of four interacting subsystems that simulate the population dynamics of the pest species, sugarcane growth, environmental dynamics, and the cost of IPM strategies, respectively.…”

“…The model boundary was chosen to be one hectare (100 m × 100 m) of continuous simulation space. There are approximately 130,000 sugarcane stalks per hectare in a typical sugarcane field in South Africa (Conlong, 2014(Conlong, -2016. This is deemed suitable to provide enough complexity for prevailing behavior and population dynamics to become evident in the simulation, while still not cluttering the simulation space and overcomplicating analysis and investigation.…”

“…Larvae that do not perish proceed to disperse among the sugarcane stalks. Conlong (2014Conlong ( -2016 describes a behavior whereby larvae move up the stalk near the oviposition site and "parachute" from the green leaf tips to surrounding plants. This results in localized dispersion within the local area surrounding the site where eggs were oviposited.…”

“…Modeling of this part of the larval life stage begins with the larva searching in its immediate vicinity for the closest sugarcane stalk into which to bore (Conlong, 2014(Conlong, -2016. The larva then moves toward this selected stalk and attempts to burrow into it.…”

“…These include sugarcane variety development (Conlong & Rutherford, 2009;Keeping & Rutherford, 2004), chemical control (Heathcote, 1984), and biological control. Habitat management (Conlong, 1990(Conlong, , 2014(Conlong, -2016Conlong & Rutherford, 2009) and the sterile insect technique (SIT) (Potgieter, van Vuuren, & Conlong, 2016) are in the research phase as part of the further development of SASRI's area-wide integrated pest management programme (AW-IPM). 1 IPM systems aim to combine a series of control methods in order to achieve better overall pest management while decreasing the use of pesticides, thereby decreasing associated environmental problems.…”