A Temperature-dependent Matrix Model for the Population Dynamics of Aculops pelekassi (Acari: Eriophyidae)

Abstract

Pink Citrus Rust Mite, Aculops pelekassi (Keifer), is an important Eriophyoid pest (Acari: Eriophyoidae) in the citrus orchards of Jeju, Korea. The most damages occur on fruits resulting in serious economic losses. This study was carried out to develop a temperature-dependent matrix model that can be used for the projection of the population dynamics of A. pelekassi in citrus orchards. The temperature-dependent development and fecundity of A. pelekassi were investigated, and biological parameters were estimated to construct the matrix model. Egg development times decreased with increasing temperature and ranged from 6.59 d at 16→ to 1.93 d at 35→. Total development times of nymphs decreased from 8.18 d at 16→ to 3.30 d at 35→. The egg to adult durations were 14.76, 11.59, 9.71, 8.03, 7.32, 6.13, and 5.23 d at 16, 20, 24, 26, 28, 32, and 35→, respectively. By fitting linear models to the data the lower developmental threshold temperatures for eggs, nymphs, and total (egg + nymph) were calculated as 9.30, 4.33, and 6.68→, respectively. The thermal constants were 54.00, 101.76, and 153.84 degree-days for each of the above stages. The non-linear model was based on a biophysical model, which well fits the relationship between development rate and temperature for all stages. The Weibull function provided a good fit for the distribution of development times of each stage. Adult longevity decreased with increasing temperature and ranged from 24.17 d at 16→ to 14.60 d at 35.0→. A. pelekassi had a maximum fecundity of 33.07 eggs per female at 28→, which declined to 18.75 eggs per female at 16→. Also, three temperature-dependent components for an oviposition model of A. pelekassi were developed including models for total fecundity, age-specific cumulative oviposition rate, and age-specific survival rate. A temperature-dependent matrix model was developed to analyze the population dynamic of A. pelekassi, based on the above experiment data. The age class of A. pelekassi was categorized into three stages: egg, nymph and adult. Transition probabilities from an age class to the next age class or the probabilities of remaining in an age class were obtained from development rate function of each stage (age classes). The fecundity coefficients of adult population were estimated by the product of adult longevity completion rate (1/longevity) and temperature-dependent total fecundity. Model outputs showed the typical form of exponential population growth. The matrix model outputs were compared with the actual field data in 2007, to test its validation ability. On leaves in early season, the model outputs pursued the actual population of A. pelekassi during a considerable days ≒20 d. On fruits in mid-season, however, the model outputs showed a larger discrepancy with the actual. The sensitivity of the model outputs to temperature changes was examined by running the model with temperatures increased or decreased by 3→ from 30 yr average air temperatures. The model outputs flexibly responded to changing temperatures. Also, the limitation and further improvement of the matrix model were discussed.