Weather events such as drought and elevated atmospheric CO2 are likely to interact with plants in numerous ways with diverse mechanisms. As a consequence of changes in quality of plants, the performance parameters and population dynamics of herbivores are expected to be influenced. In this study, a split-plot design was used to evaluate the interaction of elevated CO2 and irrigation regime on population growth of the two-spotted spider mite, Tetranychus urticae Koch (Tetranychidae: Tetranychini), feeding on sweet pepper, Capsicum annum L. (Solanaceae), in environmentally controlled chambers. Results showed that exposure to elevated CO2 significantly increased the C/N ratio in sweet pepper plants. Except in case of the adult stage, elevated CO2 did not significantly increase the population density of other developmental stages or the overall population of T. urticae. However, water stress by itself and in combination with elevated CO2 had significant effects on per capita population growth rate (r) and population density of mites. Maximum growth rate and population density of mites were observed at a combination of elevated CO2 and intermediate water stress. Further studies, especially in field conditions, investigating the impact of elevated CO2 and water stress on population size and growth of herbivores in other plant species may contribute to a greater understanding of the implications of global climate change on future crop productivity.

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