Ecological, behavioural and nutritional factors influencing use of palms as host plants by a Neotropical forest grasshopper

Abstract

ABSTRACTThis study focused on relationships between a tropical forest grasshopper and a major group of its host plants. Microtylopteryx hebardi (Acrididae:Ommatolampinae) at La Selva Biological Station, Costa Rica, feeds on understorey palms as well as other understorey plants. We assessed leaf damage levels in populations of three geonomoid palm species (Geonoma cuneata, Geonama congcsta, Asterogyne martiana), investigated feeding response of M. hebardi to the three palms, and examined leaf characteristics presumed to be important to herbivores. In understorey and gapedge habitats, total leaf damage did not differ significantly between palm species. In the centre of small light gaps, where M. hebardi was most abundant, total leaf damage and total herbivory on G. cuneata was equal to that on the other species, but herbivory attributable to grasshoppers was significantly greater. Female M. hebardi showed strong preference for G. cuneata over the other palm species in laboratory feeding trials. Experiments to elucidate the proximate basis for this feeding preference showed that grasshoppers preferentially bit filter paper discs containing cuticular wax extract of G. cuneata. In consumption and digestibility experiments, grasshoppers consumed more fresh weight of G. cuneata and gained more weight per unit time spent feeding on this species. Leaves of G. cuneata had the highest percentage water content, highest fresh and dry mass per unit leaf area, and the lowest percentage crude lignin among the three palms studied. These factors may partially explain the preference of M. hebardi for G. cuneata, which was reflected in higher herbivory rates incurred by G. cuneata in sites where M. hebardi was locally abundant.