Estimating insect population density from trap counts

Trapping is commonly used in various pest insect monitoring programs as well as in many ecological field studies. Despite this, the interpretation of trap counts is challenging. Traps are effective at providing relative counts that enable comparisons but are poor at delivering information on the absolute population size. Making better use of trap data is impeded by the lack of a consistent underlying theoretical model. In this paper, we aim to overcome current limitations of trapping methods used in ecological studies through developing a theoretical and methodological framework that enables a direct estimate of populations from trap counts. We regard insect movement as stochastic Brownian motion and use two different mathematical approaches accordingly. We first use individual-based modelling to reproduce trap catch patterns and study the effect of individual movement on observed catch patterns. We then consider a ‘mean-field’ diffusion model and show that it is capable of revealing the generic relationship between trap catches and population density.