LONG-TERM POPULATION-DYNAMICS OF THE INDIAN MEAL MOTH PLODIA-INTERPUNCTELLA AND ITS GRANULOSIS-VIRUS

1. Theoretical studies suggest that disease may play an important role in the population dynamics of insects, but there have been no long-term empirical studies that have examined this interaction in the absence of other important biotic and abiotic factors. 2. In the laboratory, three virus-free (VF) populations of Plodia interpunctella were compared with three virus-infected (VI) populations that were continuously exposed to a granulosis virus. Data sets lasted for between 10 and 17 generations. Census data of dead adults were collected twice weekly and spectral analysis of the data was used to complement the observed population fluctuations. 3. The VF populations exhibited discrete cyclic fluctuations with a period slightly in excess of one generation's length. However, the cycle period decreased significantly in later cycles in all three cases. 4. The VI populations also exhibited discrete cycles, but with a period significantly longer and a population density significantly reduced compared with the VF populations. The VI populations exhibited no change in cycle period during the period of observation. The dynamics of the pathogen itself were highly unstable and there was little evidence for linked host-pathogen fluctuations. 5. The cyclic fluctuations in the VF and VI populations appeared to be caused predominantly by density-dependent larval competition for food, whilst the pathogen was thought to be responsible for the fundamental differences between the populations.