To the Editor: Author(s): Hugh J. Barclay and Marc J. B. Vreysen Source: Journal of Economic Entomology, 106(5):1939-1939. Published By: Entomological Society of America URL: http://www.bioone.org/doi/full/10.1603/EC13053

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LETTERS TO THE EDITOR J. Econ. Entomol. 106(5): 1939 (2013); DOI: http://dx.doi.org/10.1603/EC13053 TO THE EDITOR: Peck and Bouyer (2012) have written an essay to apprise tsetse modelers regarding which kinds of models are useful and which are not. It seems that they do not like much of what has gone before in the insect modeling world. An overview of tsetse modeling is welcome and they make some good points. However, there are enough inconsistencies in their presentation that a response is warranted. Peck and Bouyer single out two approaches to tsetse modeling and label both as inadequate. These two are those of the Hargrove, Vale, and Torr group and the tsetse model published by us (Barclay and Vreysen 2011). Hargrove et al. (2011) have pointed out various problems with our article; we have since addressed all the concerns of Hargrove et al. and have updated the model with a more realistic dispersal component and time step. An article has recently been published (Barclay and Vreysen 2013) based on these changes that addresses the effects of dispersal on the ease of control of tsetse. Peck and Bouyer cite many publications of Hargrove and his associates and note (quite rightly) that they represent some of the best modeling of tsetse yet done. However, they later single out his approach as being inadequate because it does not consider spatial effects. In fact, Hargrove and his group have used both diffusion equations and probability distributions in assessing the effects of spatial distribution on tsetse population dynamics, and hence control. Peck and Bouyer refer to efforts at modeling spatial effects using diffusion equations as deserving special attention. In fact, diffusion equations are useful in some circumstances (modeling heat transfer along a metal rod, Brownian motion, large-scale movement of animals, etc.), but have severe limitations when used in an ecological context. They assume that all particles (in this case, insects) move randomly and independently. Some species may approximate this, but tsetse ßies spend a signiÞcant amount of time resting, either sleeping off a large bloodmeal or waiting for a larva to Þnish development and be born; they also appear to exhibit some Þdelity to a home range. In addition, diffusion equations in their simplest form have only one parameter and so only one factor can be modeled by them, although the addition of net movement (drift) allows another parameter to be used. Further, this one parameter has units of distance squared per unit time, and this is almost un-interpretable in an ecological context. Peck and Bouyer then go on to decry the use of simplistic models that are biologically

unrealistic, which seems contradictory after they have referred to the diffusion models as deserving special attention. Peck and Bouyer claim that we have argued for the use of the sterile insect technique (SIT) as being necessary or highly desirable in tsetse control. Although we do both believe that SIT is a very valuable tool for pest control and it should not be hastily dismissed from the arsenal of control methods for tsetse, our model is designed to allow the user to test the efÞcacy of the four methods included in the model, both singly and in combination, and to allow the user to determine which ones would be optimal in a given situation. Peck and Bouyer note that different models that give similar results lend conÞdence in the robustness of the result. This is indeed a valuable approach to assessing how realistic are the results of a particular model. However, Peck and Bouyer then conclude that the various approaches that have been used so far are so different that they cannot be used for assessing robustness. This appears contradictory, as great similarity of two models would be expected to yield similar results and could not be construed as an index of robustness (Peck and Bouyer 2012, p. 1482). We were criticized for not making the model code available. We intend to put the code on the Web along with the model in the near future. References Cited Barclay, H. J., and M.J.B. Vreysen. 2011. A dynamic population model for tsetse (Diptera: Glossinidae) area-wide integrated pest management. Popul. Ecol. 53: 89 Ð110. Barclay, H. J., and M.J.B. Vreysen. 2013. The interaction of dispersal and control methods for the riverine tsetse ßy Glossina palpalis gambiensis (Diptera : Glossinidae): a modelling study. Popul. Ecol. 55: 53Ð 68. Hargrove, J., S. Torr, and G. Vale. 2011. Comment on Barclay and Vreysen: published dynamic population model for tsetse cannot Þt Þeld data. Popul. Ecol. 53: 413Ð 415. Peck, S. I., and J. Bouyer. 2012. Mathematical modeling, spatial complexity, and critical decisions in tsetse control. J. Econ. Entomol. 105: 1477Ð1486.

Hugh J. Barclay 928 Old Esquimalt Road Victoria, B.C., Canada V9A 4X3 Marc J. B. Vreysen Insect Pest Control Laboratory Joint FAO/IAEA Programme of Nuclear Techniques in Food and Agriculture International Atomic Energy Agency Vienna, Austria

0022-0493/13/1939Ð1939$04.00/0 䉷 2013 Entomological Society of America

Which kinds of models are useful and which are not.

Which kinds of models are useful and which are not. - PDF Download Free
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