Individual-based modelling of population dynamics and evolution of resistance to phospine in lesser grain borer

The aim of this study is to use individual-based two-locus simulation modelling to predict population dynamics and the evolution of resistance to phosphine (PH3) fumigation in the lesser grain borer, Rhyzopertha dominica, and thus significantly contribute to evaluating resistance management strategy options. Individual-based modelling is a cutting-edge approach that explicitly represents the fact that R. dominica populations consist of individual beetles, each of a particular genotype and a particular life stage. Four numerical algorithms for generating or estimating key parameters within such models are described first in Chapter 2. The results of numerical experiments demonstrated that the developed algorithms are valid and efficient. In Chapter 3, two- and four-parameter probit models for phosphine mortality estimation within a two-locus resistance simulation model (which comprises nine possible genotypes) are developed. These probit models fit extensive experimental data very well and include mortality predictions that vary with concentration, exposure time, and genotype. In Chapter 4, the differences between the predictions of one- and two-locus individualbased models are compared in three cases: in the absence of phosphine fumigation, and under high and low dose phosphine treatments. Simulation results show the importance of basing resistance evolution models on realistic genetics and that using oversimplified one-locus models to develop pest control strategies runs the risk of not correctly identifying tactics to minimise the incidence of pest infestation. In Chapter 5, the individual-based two-locus model is used to judge the management tactics of single phosphine fumigation by investigating some biological and operational factors that influence the development of phosphine resistance in R. dominica.