POPULATION-DYNAMICS OF THE INDIAN MEAL MOTH - DEMOGRAPHIC STOCHASTICITY AND DELAYED REGULATORY MECHANISMS

1. Laboratory populations of the Indian meal moth [Plodia interpunctel la (Hubner) (Lepidoptera: Pyralidae)], undergo sustained periodic fluc tuations in abundance. The period is just longer than the generation t ime. The fluctuations are accentuated in the presence of the P. interp unctella granulosis virus (PiGV). 2. Time series spanning 8-10 generat ions from three replicate populations of the virus-free (VF) system an d three from the virus-infected (VI) system are investigated using non parametric autoregressive time series models. 3. The dynamics are conc luded to correspond to a third order process consistent with interacti ons in a three-dimensional stage-structured model for both systems. Th e functionally different interactive stages are believed to be the egg stage (preyed upon by larvae), small larvae (competing for resources and cannibalized by large larvae) and large larvae (competing for reso urces). 4. The virus is seen as a modulator of the host vital rates mo re than an independent agent in a trophic host-pathogen interaction. T he virus increases developmental time and decreases fecundity of the m oths. 5. A significantly nonlinear additive autoregressive model of or der 3 appears to give a parsimonious description of the series. 6. The demographic (birth and death) nature of the stochasticity inherent in the system is explicitly incorporated in the statistical model for th e time series by assuming an overdispersed Poisson process. The variab ility around the skeleton is found to conform closely to this assumpti on. The demographic nature of the stochasticity cannot be fully unders tood on the basis of Gaussian (least-squares) models on transformed (v ariance-stabilized) data. 7. Significant density dependencies are foun d at a 1-week lag, a 2- to 3-week lag and at a 6- to 7-week lag. These are argued to be the signatures of within-stage competition, between- stage interactions and reproduction, respectively. Negative and statis tically significant density dependence is apparent for the first two o f these. No significant negative density dependence is apparent in the lag:corresponding to reproduction. 8. The fluctuations in both the VF and VI system appear to represent limit cycles or weakly dampened cyc les clothed by Poisson demographic stochasticity. 9. The enhanced cycl es of the VI system are demonstrated to be consistent with a situation where the functional forms for the interactions are nearly the same a s for the VF, but with delay structure shifted by just less than a wee k.