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The koa looper (Geometridae: Scotorythra paludicola) is an endemic Hawaiian moth whose caterpillars feed on Acacia koa, and experience occasional outbreaks, producing vast defoliations of forests. During an extensive and ongoing outbreak of this species on the island of Hawaii, patchy defoliation of Falcataria moluccana ("albizia") was observed in the vicinity of Akaka Falls State Park, relatively distant from the main defoliation of koa, raising questions about the host range of the koa looper. To identify suitable host plants in the laboratory, we offered the koa looper foliage from five fabaceous tree species (A. koa, A. confusa, F. moluccana, Prosopis pallida, and Leucaena leucocephala), and recorded feeding and performance on these diets. Among the five tree species, only A. koa and F. moluccana were accepted as food; caterpillars on the other three species all died by the fifth day of the trial. Survival of the koa looper to pupation and adulthood on F. moluccana did not differ significantly from that on A. koa phyllodes, indicating that this tree is a suitable host, though it does not appear to be widely utilized in the field. Both oviposition preference and larval requirements are likely important determinants of the realized diet breadth for the koa looper. Additionally, development times at 19°C on A. koa and F. moluccana were nearly twice as long as at 23°C, highlighting the importance of temperature for development of this insect. [ABSTRACT FROM AUTHOR]

Native plant-herbivore interactions on islands remain understudied due to the widely discussed idea that island plants have weaker defenses than their continental relatives. In Hawaii, the native moth Scotorythra paludicola, a specialist on the native Acacia koa, can undergo outbreaks that defoliate tens of thousands of acres of native koa forest, sometimes leading to massive stand mortality. Such extreme herbivory events are expected to exert strong selection pressure for defense in A. koa. Because mature A. koa trees often re-flush juvenile true leaves after defoliation, we predict that true leaves are better defended against S. paludicola than phyllodes, consistent with the phenomenon of induced resistance. A no-choice bioassay was conducted in the laboratory to compare S. paludicola development on true leaves vs. phyllodes. Consistent with our predictions, caterpillars reared on true leaves had a significantly higher mortality rate and took longer to pupate than caterpillars reared on phyllodes. Additional sources of variation in S. paludicola development included sex, phyllode age (young vs. mature), and host tree identity. Further research is needed to determine the mechanistic traits underlying A. koa resistance to S. paludicola, and to test whether true leaf development does in fact contribute to a reduction in S. paludicola performance and population stability on previously defoliated trees. [ABSTRACT FROM AUTHOR]