The feeding biology of a species-rich genus of rainforest grasshoppers (Rhachicreagra, Orthoptera, Acrididae) : II. Foodplant preference and its relation to speciation.

1. Two geographically adjoining but allopatric and altitudinally disjunct species (nothra and anchidiphalara) of the forest grasshopper genus Rhachicreagra were compared for food plant preferences in the laboratory. It has been shown that both are oligophagous and that their natural diets are markedly different. Both were offered the same 8 foodplants in a matrix of 2-way choice experiments. These plants included all important constituents of the natural diets of both species. 2. The resultant preference rank order was virtually identical for the two species, suggesting that the proportions of the different plants in the natural diet are determined principally by their relative availability. 3. The only major differences between the rank orders of the two species arise from the fact that both show an increased preference (relative to the other species) for the commonest foodplant in their own habitat. Indirect evidence suggests that this is the result of evolutionary change, not of conditioning during the lifetime of the individual. 4. There is no suggestion that host plant switching has played any significant role in speciation within the genus.