The use of time-series analyses to understand the ecology of a foliar spider mite pest of Hass avocados

Persea mite, Oligonychus perseae Tuttle, Abatiello and Baker (Acari: Tetranychidae), is foliar pest of avocados whose colonial feeding induces premature lead drop and has been linked to yield reduction. To better understand the role of abiotic and biotic factors that might influence the populations dynamics of O. perseae, we conducted a time-series analysis for an historical 10-year data set (August 2002-2012) consisting of 120 monthly mite counts of O. perseae and phytoseiids for 17 trees (~20,400 leaves) in a non-commercial plot of Hass avocado trees in Southern California. Our statistical analyses involved four general modeling procedures: 1) building statistical models for a subset of months (e.g., 100) that account for historical average monthly temperature & humidity records from an on-site weather station; number of consecutive days where temperatures exceeded 100°F;  predatory mite densities; autocorrelated error terms and seasonality of mite densities, 2) estimating model parameters, 3) checking model adequacy using diagnostic procedures and 4) validating the model’s ability to account  for observed spider mite and predator densities with an additional 12-month period data. The results of this research provide a better understanding of the influence that weather and predatory mites have on the population dynamics of O. perseae as part of developing research-based control guidelines for this foliar pest of avocados.