Trirhabda geminata (Coleoptera: Chrysomelidae) resistance to the direct impact of simulated acidic fog on larval growth and mortality

The direct effects of acidic fog (pH 2.75) upon the mortality and growth of Trirhabda geminata Horn (Coleoptera: Chrysomelidae), the dominant herbivore of the California coastal sage scrub, Encelia farinosa (Compositae: Asteraceae), were evaluated. Although there was a consistent pattern among and between experiments, suggesting that acidic fogs could reduce insect growth and survivorship within the first few days following application of treatments, an exposure to three consecutive, 3-h fogs over a five day period did not significantly affect mortality, biomass gain, or larval growth rate. There are two important implications from this study. First, even the highly acidic fogs found in southern California will have minimal direct effects on T. geminata performance. Second, the impacts on T. geminata biology observed in previous studies were likely mediated by host-plant responses to acidic-fog episodes.