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Fern-eating forest grasshoppers of two species were studied in Costa Rica. Hylopedetes nigrithorax lives in groups on particular ferns in light-gaps. Homeomastax dentata is solitary and found throughout the forest. The relative palatability of 13 species of fern was established, including species supporting Hylopedetes colonies, species on which Homeomastax was found, and controls. The palatability scores obtained with Homeomastax were relatively closely grouped and only the least palatable plant was significantly less preferred. The scores obtained from Hylopedetes were more widely spread, and the most palatable plants were significantly preferred. This suggests that Hylopedetes is more specialised in its feeding habits, Homeomastax more generalised. The rank order of palatability to the two grasshoppers was significantly positively correlated. The proximal basis of palatability differences seems to be chemical, but the content of phenols, nitrogen, tannins and fiber showed no correlation with palatability. The siting of Hylopedetes colonies appears to be determined by sunlight and fern palatability. Most colonies are found on the most palatable fern, but the longest lived colonies occur on a less preferred species which better survives successional change. ACRIDID GRASSHOPPERS ARE USUALLY THOUGHT OF AS GENERALIST, but not indiscriminate feeders (e.g., Williams 1954, Mulkern 1967, and Gangwere 1972). There are, however, a considerable number of species which feed on only a few or even one species of plant (Joern 1979). Such grasshoppers occur in many different environments (e.g., from the temperate forests of North America, where Dendrotettix quercus eats oak leaves (e.g., Valek 1971), or Bocagella acutipennis feeding on the composite Vernonia guineensis in the west African savanna (Duviard 1970), to Paulinia acuminata eating Salvia and Pistia floating on the lakes of South America (Carbonell 1964)) and may be especially characteristic of some, such as warm temperate desert (Otte and Joern 1977) or tropical rain forest (Rowell 1978). Among the latter, several genera of neotropical grasshoppers eat ferns (Rowell 1978 and unpubl. obs.), either exclusively or as an important component of their diet along with other plants (e.g., Homeomastax, Eumastacoidea: Leptomerinthoprora, Hylopedetes, Micropaon, and Scirtopaon, Acridoidea: many tettrigids). Because ferns were among the oldest vascular plants, and Orthoptera among the oldest herbivorous insects (Smart and Hughes 1971), the relations of their modern descendants are of interest to plant/herbivore theory. To date, relatively little is known of interactions between ferns and their herbivores (see however Kaplanis et al. 1967, Cooper-Driver 1977, Gerson 1979) apart from two areas of recent research. The first of these concerns the commercially important bracken fern Pteridium aquilinum (Bernays 1977; Jones and Firn 1979a, b; Lawton 1982; Rigby and Lawton 1981; Schreiner 1980; Tempel 1981). Secondly, there has been some controversy as to whether ferns as a group suffer less from herbivory than do angiosperms (Clark 1973, Balick et al. 1978, Hendrix 1980, Auerbach and Hendrix 1980); this discussion is inhibited by the paucity of information about |
