Simulating the effects of climate change on Sitobion avenae F. (Homoptera : Aphididae) and Coccinella septempunctata L. (Coleoptera : Coccinellidae)
This study investigated how the predicted increase in global temperature would affect the interaction between the cereal aphid, Sitobion avenae F. (Hemiptera: Aphididae), and its coccinellid predator, Coccinella septempunctata L. (Coleoptera: CoccinelIidae). A model describing the summer population dynamics of S. avenae (Carter et al., 1982) was modified and updated. New equations describing the dependence of aphid development and reproduction on temperature were formulated. A new submodel, describing the population dynamics of C. septempunctata, was incorporated into the model. The predatory interaction between C. septempunctata and S. aveizae was described using a modified form of the temperature-mediated functional response equation proposed by Mack et al. (1981). A sensitivity analysis showed that the output of the model, which compared well with field observations, was not greatly affected by small changes to the parameters of the equations used in the submodel. Stochastic elements were incorporated into the model; aphid and coccinellid immigration were simulated by sampling randomly from distributions fitted to observed patterns of immigration. Three temperature regimes: hot, moderate and cold, were defined by ranking and splitting the years from 1965 to 1992 according to the mean temperature between April and August. The temperature data from the years assigned to each regime were then used to formulate an equation to describe the daily temperatures within the five months. The model was run for each regime, and the output showed that both coccinellid predation and increased temperatures caused a decrease in aphid abundance. The model also highlighted several more subtle effects of increased temperature on the interaction between S. avenae and C. septempunctata. The importance of the model predictions for future control of aphid populations in cereal crops is discussed.