Ultra-low fruit fly populations in mosaic landscapes: behavior, development, establishment and detection

Abstract

Periodic detections of medfly in areas recognized as fly-free raises a lot of theoretical and regulatory controversy. The latter can be largely reduced to the question: “how long can local populations survive in the cryptic ultra-low-density phase and remain undetected by the surveillance network”. To answer this question in the absence of empirical options, a series of stochastic simulations were carried out, emulating the behavior, development and fate of individual members of the residual / initial medfly populations. For this purpose, the PESTonFARM model was used, parameterized according to current knowledge about medfly biology and its behavior in the field conditions. The simulations were carried out for a specific area where medfly was recently detected, taking into account the key features of local topography, historical weather patterns and a surveillance system. The projections generated by the model support the hypothesis about the possibility of the prolonged existence of cryptic populations fluctuating at very low densities, which may slip out of the surveillance grids and remain undetected for longer periods of time. Analysis of various scenarios emulated by the model has revealed a number of specific environmental factors that, acting simultaneously, are able to maintain fly populations at low densities. The application of the model also allowed estimating the chances of detection for various scenarios of terrain topography, host and weather patterns.
The theoretical and practical implications of the proposed approach and methodology, its key merits and limitations, were also discussed.