An age-structured population model of citrus rust mite: a fruit–mite–fungal pathogen system

Abstract

An age-structured model of a fruit–mite–fungal pathogen system was developed to study interactions between the `Hamlin' orange fruit, the citrus rust mite (CRM) Phyllocoptruta oleivora, and its fungal pathogen Hirsutella thompsonii. The model consists of a set of difference equations incorporating the age and stage change of CRM and its fungal pathogen. The abiotic factors included in the model were daily mean temperature and daily dew period the biotic factors were mite density (egg, protonymph, deutonymph, and adult), pathogen density (latent pathogen, and infectious pathogen), and undamaged fruit surface area. One data set for the fruit–mite–pathogen dynamics was used to estimate parameters related to density-dependent CRM egg production and pathogen transmission rate. Parameters were estimated by choosing the parameter combinations which gave the least combined error sum of squares between observed and simulated populations for CRM and pathogen. For the data set used for parameter estimation, the model captured 92.2% of variation in CRM population dynamics, and 61.9% of variation in the density curve pattern of the pathogen, over a period of 5 months. Three additional data sets were used to partially test model predictability. For one data set, the model captured 87.1% of variation in CRM population dynamics, and 94.4% of variation in the density curve pattern of the pathogen, over a period of 5 months. The model, however, did not make accurate predictions for low CRM density level-pathogen interactions. The corresponding cumulative mite days and fruit surface damage were also generated by the model for each data set. With further modification and refinement, the model could be developed into a useful tool for CRM management.