Effect of Initial Population Density and Wound-Induced Plant Defence on Myzus Persicae Population Dynamics

Population density is an important ecological factor that controls rates of population growth. Population growth rate is in turn a determinant in two-species interactions, especially in species with short generation times. Aphids are the perfect example of such species, and their abundance and cheapness make them suitable model organisms for study in the laboratory. In this study, the θ-logistic growth model was utilized as a theoretical basis for analyzing population growth rates in green peach aphids feeding on Arabidopsis plants. The θ-logistic growth model predicts that population growth rates should vary with population density, but not with external environmental factors. Furthermore, to validate this model, a single environmental factor (plant defence) was altered. Plant chemical defence mechanisms, such as the jasmonic acid pathway, are induced by damage done to plants. Greater damage should induce greater response, and the extent to which defence mechanisms are activated is expected to affect plant carrying capacity. To test these hypotheses experimentally, wounded and unwounded (normal) individual plants were inoculated with increasing numbers of aphids, and aphid population was tracked over the course of several days. Population data was analyzed through regression and analysis of variation (ANOVA). Relativized population growth rates obtained from this study show that while plant damage does not appear to affect aphid growth, growth rates decreased with increasing initial population density, in accordance with the θ-logistic model.