1. Life-history differences between herbivorous insects with eruptive and
latent population dynamics are potentially useful for predicting population size
variability. An association has also been demonstrated between herbivorous insect
defence traits and the responses of various natural enemies.
2. Here predictions of population dynamics and natural enemy responses based on
life-history and defence traits are tested using Gonometa postica Walker and G.
rufobrunnea Aurivillius, two Southern Hemisphere Macrolepidoptera (Lasiocampidae)
species. The temporal and spatial variation in pupal abundance and patterns of pupal
parasitism and predation for both species are described and quantified for the first
time.
3. Eleven sites were sampled over four generations across the region where both
species have historically reached high population densities. Although there was evidence suggesting that population synchrony is driven by weather patterns, site-specific environmental differences contributed to the observed population variability. This study is the first to quantify the extent of population size variability of a species with an intermediate position on the eruptive – latent population dynamic gradient, where data on insect population dynamics is scarce.
4. Support for the life-history – population dynamic relationship was found, as
intermediate population size variability for these species was observed. Larval and pupal
defence traits, however, were poor and inconsistent predictors of mortality rate. Pupal cocoon structure differences, previously documented for these Gonometa species, may in fact explain the interspecific differences in natural enemy responses found.
5. Predicted population dynamics and natural enemy responses may, however, be overridden by ecological conditions. Nevertheless, life-history and defence traits provide a useful basis for predicting population dynamics of poorly studied species.Centre of Excellence for Invasion Biolog
