title: Modelling the effect of pyrethroid use intensity on mite population density for walnuts.
abstract: BACKGROUND
  Published studies relating pyrethroid use and subsequent mite outbreaks have largely been based on laboratory and field experiments, with some inferring a result of increased miticide use. The present study derived a mathematical model proposed to quantify the effect of pyrethroid use intensity on mite population density. The model was validated against and parameterized with actual field-level pyrethroid and miticide use data from 1995 to 2009 for California walnuts, where the miticide use intensity was a proxy of the mite population density.
  
  
  RESULTS
  The parameterized model was MI = 1.61 - 0.89 · exp(-93.31PI) (RMSE = 0.13; R(2) = 0.69; P < 0.01), where PI and MI are the average pyrethroid and miticide use intensity in small intervals respectively. A three-range scheme was presented to quantify pesticide applications based on the change rate of MI to PI. Specific for California walnuts, the PI range of 0-0.025 kg ha(-1) was identified as the rapidly increasing range where MI increased vastly when PI increased.
  
  
  CONCLUSIONS
  Results confirmed that more miticide was used, presumably to prevent or control mite resurgence when pyrethroids were applied, a practice that is not only costly but might be expected to aggravate mite resistance to miticides and increase risk associated with these chemicals to the environment and human health.
authors.affiliation: Department of Land, Air and Water Resources, University of California, Davis, CA, USA.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhan
authors.forename: Siqi
authors.initials: S
authors.lastname: Fan
authors.forename: Minghua
authors.initials: M
authors.lastname: Zhang
authors.forename: Frank
authors.initials: F
authors.lastname: Zalom
mesh_terms: D000818:Animals; D031324:Juglans; D008925:Mites; D008954:Models, Biological; D011156:Population Density; D011722:Pyrethrins; D012044:Regression Analysis
chemical_list: D011722:Pyrethrins
keywords: integrated pest management; mite; miticide; pyrethroid; walnut