INTERACTIONS BETWEEN OPEROPHTERA-BRUMATA AND TORTRIX VIRIDANA ON OAK - NEW EVIDENCE FROM TIME-SERIES ANALYSIS

1. Yearly population estimates of the green oak leaf roller moth, Tort rix viridana (Lepidoptera: Tortricidae), and the winter moth, Operopht era brumata (Lepidoptera: Geometridae), were taken from the pedunculat e oak, Quercus robur, from 1951 to 1966 in Wytham Woods, Oxfordshire, U.K. Larval mortality from parasitoids was recorded for both species o ver the same period. 2. Operophtera brumata population density fluctua ted around a constant mean, whereas I viridana population density exhi bited a linear decline over the sampling period. Population counts wer e subjected to time-series analysis after the linear decline was remov ed from the T. viridana data by detrending. Multiple regression models were built so that variation in the per capita rate of increase of ea ch population could be partitioned among (a) current and previous popu lation density, (b) current and previous population density of the sec ond moth species, and (c) rates of larval parasitism. 3. Multiple regr ession analysis suggested that variation in the per capita rate of inc rease of O. brumata could be explained by negative feedback from O. br umata density at T-2 (32%), a negative relationship with I viridana de nsity at T-l (18%), and a positive relationship with parasitism suffer ed by I viridana at T-l (24%). 4. The I viridana population time-serie s was dominated by a rapid feedback process such that per capita rate of increase at time T was negatively related to population density at time T-l, explaining 53% of variance in population growth rate. Per ca pita rate of increase was unrelated to larval parasitism or densities of O. brumata. 5. In light of previous life-table and experimental stu dies on O. brumata and I viridana, the current analyses suggest that p upal predation (data not presented) and interspecific competition are significant determinants of O. brumata population growth rates in Wyth am Woods. In contrast, T. viridana population growth rates appear to b e dominated by rapid negative feedback consistent with intraspecific c ompetition.