Modelling the proximal source of intercepted exotic insects

Abstract

Biological invasions are major threats to any nation’s economy and biodiversity. To detect new biological incursions of some species biosecurity agencies deploy pheromone sentinel traps for targeted species at high risk sites such as airports, seaports and transitional facilities. A good example is the gypsy moth surveillance program in New Zealand. Following the detection of an incursion by an unwanted organism, ground-based searches to locate the source can be very expensive, but are essential to identify the introduction pathway and to increase the chances of success eradicating the unwanted organism. In such circumstances, the possibility of better targeting the search for the source of the incursion using a modelling approach is worthy of investigation A stochastic mechanistic model to hindcast moth flight from a recapture location to the release location was developed based on insect behaviour in response to wind and pheromones. The model was composed of two main processes, 1) downwind dispersal, assumed to result from an appetitive behaviour, indicated by an analysis of a previous mark-release-recapture experiment on painted apple moth (Teia anartoides, Walker) and, 2) anemotaxic dispersal inspired by pheromone anemotaxis theory but up-scaled from a fine-scaled behaviour model to a 2 m scale.

A genetic algorithm was used to fit some model parameters. A specialised fitness function was developed to allow the genetic algorithm to identify parameters that resulted in models that reflected both the spread and density patterns in the trapping data. The resulting function allowed the stochastic model results to be compared with the inherently stochastic trapping data. The resulting individual based model simulates the spatio-temporal dispersal pattern of painted apple moth recorded during a previous mark-release-recapture experiment. While the proposed model is shown to have limitations with respect to accuracy and precision it is also demonstrated to greatly improve biosecurity incursion response capability, by more efficient targeting of search effort for the proximal source of an incursion.