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Modelling the effect of pyrethroid use intensity on mite population density for walnuts
Yu Zhan1, Siqi Fan, Minghua Zhang
1Department of Land, Air and Water Resources, University of California, Davis, CA, USA.
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.
Conclusion:
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.
Insights
Increased pyrethroid pesticide use in walnuts leads to greater miticide application, potentially worsening mite resistance and environmental risks. This study models the pyrethroid-miticide use relationship.
Area of Science:
- Agricultural Entomology
- Pest Management
- Chemical Ecology
Background:
- Previous studies on pyrethroid use and mite outbreaks relied on experiments.
- A gap existed in quantifying the direct impact of pyrethroid intensity on mite populations.
- This research addresses the need for quantitative models in pest management.
Purpose of the Study:
- To develop and validate a mathematical model.
- To quantify the relationship between pyrethroid use intensity and mite population density.
- To analyze pesticide use patterns in California walnuts.
Main Methods:
- Derived a mathematical model linking pyrethroid use intensity (PI) to miticide use intensity (MI).
- Validated and parameterized the model using 15 years of field data from California walnuts.
- Defined a three-range scheme to categorize pesticide application based on MI change rate relative to PI.
Main Results:
- The model MI = 1.61 - 0.89 · exp(-93.31PI) accurately described the relationship (R² = 0.69).
- A pyrethroid use intensity range of 0-0.025 kg ha⁻¹ was identified as critical, showing rapid increases in miticide use.
- Higher pyrethroid application correlated with increased miticide use, indicating a cycle of pest control escalation.
Conclusions:
- Pyrethroid application necessitates increased miticide use to manage mite resurgence.
- This practice incurs costs and risks aggravating mite resistance to pesticides.
- Increased chemical use poses greater environmental and human health risks.
