Changes in Saponins and Tannins in Ripening Holly Fruits and Effects of Fruit Consumption on Nonadapted Insect Herbivores

Abstract

-Secondary compounds in fruits are thought to be a defense against invertebrates or pathogens which might otherwise damage or destroy the fruits or seeds without contributing to seed dispersal. We incorporated ground, nonripe green or ripe red fruits of American holly Ilex opaca into standard diets of two species of polyphagous caterpillars to test the hypothesis that nonripe fruits are better defended than ripe fruits. Fall armyworm Spodoptera frugiperda larvae grew more slowly on diet augmented with 10% (dry wt) ripe fruits than on control diet with 10% cellulose powder, and slower still on diet with nonripe fruits. However, survival, pupal weight and length of the pupal period were not affected by either treatment. Growth rates and survival of fall webworms HIyphantria cunea were reduced to a similar degree by both nonripe and ripe fruits. Methanolic extracts of nonripe fruits brushed on leaf disks of sassafras, a preferred host, deterred feeding by Japanese beetles Popillia japonica Newman, a highly polyphagous species. Extracts of ripe fruits were not repellent. Saponin content was highest in nonripe green fruits, while tannin levels were highest in ripening fruits. In choice tests, red holly fruits were removed from bird feeders at a faster rate than nonripe green fruits. Levels of secondary compounds in fruits of I. opaca may be a compromise between the continued need to protect the seeds from predispersal damaging agents without deterring potential vertebrate dispersers.