Density dependence and noise determine the long-term dynamics of two species of lady beetle (Coleoptera: Coccinellidae: Epilachninae) in the Indonesian tropics

1. The long-term dynamics of two beetles (Epilachna vigintioctopunctata and Epilachna enneasticta) from Indonesia are analysed using descriptive time-series statistics and mechanistic time-series models. 2. Statistical analysis of the time series reveals that the dynamics of E. vigintioctopunctata are underpinned by a second order density-dependent [AR(2)] process, which is consistent between sites. Similarly, the dynamics of E. enneasticta are also described by a second order density-dependent [AR(2)] process. The predicted dynamics from these statistical models are stable dynamics. 3. Mechanistic models of the density dependence predict that in the absence of noise the dynamics of the populations should also be stable. Inclusion of the stochasticity in the models of density dependence allows a more accurate description of the population dynamics of each species to be determined. 4. Correlation analyses reveal that the fluctuations between species are a function of both the density dependence and the environmental conditions experienced by each species. Under low environmental variance it is predicted that the dynamics could be synchronised but under high variance in environmental noise, the dynamics may not be synchronised and species respond idiosyncratically to the environment. 5. The study highlights the value of long-term population dynamic time series for exploring the structure of population regulation and fluctuations in insect populations. © 2006 The Royal Entomological Society.