Predation by Insects Limits Seed Production in Banksia spinulosa var neoanglica (Proteaceae)

Abstract

Application of insecticide to inflorescences of Banksia spinulosa var. neoanglica indicated that damage by flower and seed predators halved the number of seeds produced per plant. Both the proportion of inflorescences that produced fruits and the number of seeds produced per infructescence increased by 45% when insects were excluded. Infructescences in the insecticide treatment produced 28% more follicles than in the control group. Insects damaged the seed in 13% of follicles in the control group whereas there was no damage in the insecticide treatment. The proportion of follicles with aborted seed did not differ between the two groups. The greater seed set occurring when insects were excluded did not affect the weight of individual seeds or reproductive output in the next flowering season. Some inflorescences did not produce fruit even when insects were excluded suggesting that factors besides predation also limit fecundity of B. spinulosa.