SEED SET AND SEED PREDATION IN PEDICULARIS FURBISHIAE, A RARE ENDEMIC OF THE ST. JOHN RIVER, MAINE

We measured seed set and losses due to mammal and insect predation during 1983 in seven northern Maine populations of Furbish's Lousewort ( Pedicularis furbishiae S. Wats.; Scrophulariaceae), a perennial herb endemic to the banks of the St. John River. Only about a quarter of initiated flowers developed a capsule with a full complement (mean = 25) of seeds. Secondary (lateral) inflorescences matured a smaller proportion of capsules than primary (terminal) inflorescences. About 58% of the initiated flower primordia were aborted or did not develop mature seeds by early September; this was probably not due to pollinator limitation. Several agents could have reduced seed production. Although spittlebugs infested between 3 and 30% (average 20%) of developing flower scapes by population, they did not depress the number of inflorescences initiated or the number of capsules matured. In contrast, 74% of capsules containing a lepidopteran seed predator (the plume moth Amblyptilia pica [Walsingham], newly discovered as a seed predator on P. furbishiae ) had no seeds (mean = 3 seeds). Seed predation affected 39% of the potentially maturable capsules. In 6–30% of all capsules preyed upon, the lepidopteran was parasitized by an ichneumonoid wasp larva; these capsules matured about 7 seeds. Herbivory by rabbits, rodents, and deer also reduced seed set, eliminating 98% of the scapes at one site, and averaging 40% for other populations. Mammals and insects together removed at least 62% of maturable seeds. Populations varied widely in predation and seed set. Predispersal seed loss in P. furbishiae, coupled with slow seedling growth and occasional catastrophic mortality from ice scour and erosion, could limit population growth in this rare endemic.