Seasonal population dynamics of the European red mite (Panonychus ulmi) and its predator Neoseiulus californicus in a sprayed apple orchard in Argentina (Acari: Tetranychidae, Phytoseiidae)
1995 - Volume: 36 Issue: 4 pages: 325-331
prey predator interaction
Seasonal population dynamics of tetranychid and phytoseiid mites were studied in a chemically treated apple orchard, in the south-eastern region of Buenos Aires Province. Seventy-five Red Delicious apple leaves per tree were collected monthly, from November 1990 to March 1993. Abundance and prevalence were calculated for each sample. Three differential pesticide applications were made during this period twice a month (1990/1991), once a month (1992/1993) and no applications (summer 1991/1992). Panonychus ulmi (Koch) was the only species of Tetranychidae found, and Neoseiulus californicus (McGregor) the only phytoseiid present in the orchard. This low diversity revealed the important influence of pesticides. Fluctuations of phytophagous and predatory mites were analysed for each sampling period, and comparisons between them revealed that periods with strong pesticide applications showed decreases of N. californicus populations and outbreaks of P. ulmi populations, supporting the Predator Inhibition Hypothesis . Conversely, months that were left free from spraying, showed high abundances, of N. californicus and decreasing phytophagous populations. Fluctuations of P. ulmi prevalence were similar to those of abundance. Summer climatic conditions and pesticides (including the pesticide resistance of P. ulmi) are the main factors affecting the seasonal population dynamics of the mite species studied.
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