COS 8-6
Mechanisms maintaining two feeding strategies in the moth Symmestrischema lavernella
Traditional explanations for specialized host use patterns by herbivores include evolving to use high quality plant hosts, avoid natural enemies and make efficient use of the most common food resource in the environment. While several studies have combined two of these hypotheses, we are still in need of understanding how an increasing number of factors interact to determine herbivores’ diets. Symmetrischema lavernella is a phytophagous gelechiid moth whose hosts appear to be limited to the genus Physalis (Solanaceae). Flower buds and fruits serve as larval substrates producing budworms and frugivores, respectively, and both strategies are used in each of the 3+ generations of the moth. However, each larva can adopt only one strategy, leading to the prediction that the most profitable strategy should persist over time. Alternatively, frugivores and budworms would coexist if selective pressures render both strategies similar in costs and benefits or show enough variation to impede fixation on the preferred strategy. This study was aimed at explaining the occurrence of these two feeding strategies in S. lavernella by assessing the effect of food quality, mortality inflicted by natural enemies and resource availability under varying moth densities through field observations and experiments.
Results/Conclusions
Pupal weights of frugivores were found to be 33% greater than those of budworms, with females being heavier for both feeding strategies. Frugivores also showed greater survival than budworms in natural patches of their host plant, despite 69% of parasitoid attacks being observed in frugivores. Upon exposure of plants to varying densities of moths, budworms occurred when density of adults was high, suggesting this strategy may reduce intraspecific competition. Together, these results imply tradeoffs between performance, survival and competition may maintain both feeding strategies in S. lavernella.