The model described in this paper simulates seasonal dynamics of Panonychus ulmi and the phytoseiid predator Typhlodromus pyri on apple trees in Eastern North America. It was originally developed to understand the effect of weather, predation, cannibalism, alternate food for the predator, and uneven mite distribution among leaves on mite dynamics. Overwintering mortality of T. pyri, cannibalism, and the uneven distribution of predators and prey among leaves were found to stabilize the predator/prey interaction. The availability of alternate foods for T. pyri minimizes the likelihood of predator extinction at the whole-tree level, as is seen in orchards. The model was used to guide tactics of mite management. Early simulations involving optimal times to apply miticides indicated that if there are high densities of P. ulmi winter eggs, and mite counts are not done until June, there would be significant damage before the mites are noticed and treatments applied. This insight was relayed to growers who now monitor P. ulmi eggs in April and apply treatments if needed to prevent early-season damage. Growers also accepted simulations which suggested that post blossom applications of the miticide Apollo would be more effective than applications made before bloom. Other simulations validated the empirical decision rule that biological control is effective with a T. pyri: P. ulmi ratio of at least 1:10. The model also indicated the value of introducing T. pyri into orchards early in the summer to maximize speed of colonization and biological control. Finally, the model has served to guide research. Discrepancies between simulated and observed densities of mites were usually due to factors not yet included in the model such as aerial dispersal of adult P. ulmi, leaf quality, sublethal effects of pesticides on T. pyri, feeding competition among predators, and availability of alternate food for T. pyri. Considerable research has been done on these factors.
|Title of host publication||Computer Modelling in Fruit Research and Orchard Management : proceedings of the 5th International Symposium|
|Editors||P.S. Wagenmakers, W. van der Werf, P. Blaise|
|Publication status||Published - 1999|