Characteristics of Pseudacteon tricuspis Borgmeier (Diptera: Phoridae) population spread in Louisiana
Donald C. Henne, DHenne@agcenter.lsu.edu and Seth J. Johnson, SJohnson@agcenter.lsu.edu. Louisiana State University Agricultural Center, Department of Entomology, 404 Life Sciences Building, Louisiana State University, Baton Rouge, LA
Knowing organism spread rates are important for predicting future movements into new areas based on previous dispersal patterns. Animal populations follow either a constant or accelerating pattern of expansion when square root of area occupied is plotted against time. We studied expansion of two Louisiana Pseudacteon tricuspis populations from 1999 to 2005. By disturbing Solenopsis invicta mounds in four directions (north, south, east and west) from each release location and determining presence/absence of P. tricuspis, we approximated yearly spread limits. We found that the square root of area occupied by P. tricuspis over time is described by a quadratic function, indicating that P. tricuspis population expansion in Louisiana follows a stratified dispersal pattern, i.e. local (neighborhood) diffusion and long-distance dispersers. Over time some individuals disperse far ahead of the advancing surface wave and establish nascent far-flung colonies which spread in similar fashion to the parent colony, and an accelerating (quadratic) expansion pattern results. Our P. tricuspis populations exhibit a latent phase where dispersal is slow for several years, followed by accelerating spread to an asymptotic rate of approximately 16-27 km/year, depending on direction from the release areas. Spread patterns were anisotropic with respect to position of the release point: slower south and faster north. A putative explanation is that flies are being transported farther north in sea breezes blowing south to north along the Gulf coast during the summer months.
Species 1: Diptera Phoridae Pseudacteontricuspis (fire ant decapitating fly)