Instructional Simulation: Sterile Insect Release Method with Spatial and Random Effects

Abstract

A simulation model of the sterile insect release (SIR) method of population suppression was developed as a modeling exercise by advanced students of integrated pest management (IPM). Objectives were to create an instructional model that would demonstrate the principles and operation of the SIR technique to undergraduate IPM students, and allow users to see the effects of relaxing or violating various assumptions of the basic model. In particular, the influence of dispersal, spatial distribution of wild and sterile insects, uncertainty about the initial population density, and stochastic processes can be examined by simulation. Ease of changing the qualitative structure of the model and quantitative values of parameters, along with rapid execution and graphic display on a microcomputer, enhance the instructional value of the model. Simulations show that adjustment of the number of sterile males released can generally compensate for variations in competitiveness of sterile males and uncertainty about the survival rate, fecundity and sex ratio of wild insects. However, dispersal and spatial heterogeneity of the target population place more severe demands on the technique. Release of sterile males in a buffer zone surrounding an isolated population is necessary whenever dispersal is likely, but high mobility of the target species and economic and practical considerations may limit the feasibility and success of this approach. Release ratios that greatly exceed expected necessary levels may fail to ensure eradication due to variations in local pest density and sampling errors. Inadequate detection methods may add to the difficulty of eradicating mobile pests. Knowledge of emigration probabilities and dispersal distances, carefully designed sampling and release programs that take spatial heterogeneity of density into account, and efficient detection methods are all essential to success of the SIR technique.