Leaf shelter building is a common behavior in different orders of herbivorous insects. Among proposed shelter functions are protection against predators, and the improvement of both environmental conditions and leaf’s nutritional quality. The aim of this study was to evaluate costs and benefits of shelter building behavior of Gephyra cynisca (Pyralidae) on the leaves of its host Piper stipulaceum (Piperaceae). Specifically, we assessed petiole trenching impact on food quality and shelter’s anti- predator function. This study was conducted in a tropical dry forest located in Jalisco, Mexico. To evaluate trenching effects on food quality, two comparisons of larval performance (pupal mass and developmental time) were made: a) between individuals fed on 3- days trenched leaves vs. recently trenched leaves, b) between individuals fed on recently trenched leaves vs. non trenched leaves. To asses the shelter’s anti- predator function, a pairwise experiment was performed in which caterpillars were placed either inside a refuge or exposed on a leaf while building the shelter (4 hours approx.). Predation rates were compared between treatments. To measure physiological costs of shelter building, performance of larvae constructing none, one or many shelters during their lifetime was compared.
Caterpillars fed with recently trenched leaves developed faster than caterpillars fed with 3- days trenched foliage, but larvae on both treatments attained the same pupal mass. In contrast, developmental time of caterpillars fed with trenched foliage was equal to that of caterpillars fed with non trenched foliage. In this case, pupal mass was found to be larger in the caterpillars of the trenched treatment. Survival after the predation experiment was significantly higher in sheltered caterpillars than in the exposed ones. In addition, no physiological costs were found with the shelter building experiment because developmental time and pupal mass did not differ significantly among shelter construction treatments. These results show that trenched shelters first enhance food quality of P. stipulaceum for G. cynisca, but then it decays as time passes because foliar tissue dries out. However, the mechanism underlaying leaf quality improvement is not clear, as trenching may prevent importing defenses as well as exporting nutrients by the leaf. Shelters also improved survival because they lowered predation probability. Although we found no evidence of physiological costs of shelter building, we found a predation cost because during this process caterpillars are more conspicuous. In conclusion, we found that Gephyra cynisca´s shelters provide anti-predator protection and also improve leaf nutritional quality.